Remember, that like so many natural health approaches, what may provide the most immediate temporary relief from an allergy attack, (for example, a botanical), may not be the best long-term solution for resolving the issue...such as addressing your gut flora, or your liver, or adrenals, or your balancing your immunity.
1. DDS-1 Probiotics
I have used these strains of probiotics since 1993 to quickly and effectively reduce histaminic responses like those described above. Like different dogs, different strains of probiotics, though they may be the same species, can vary greatly in their attributes. I have repeatedly found that for histaminic seasonal allergies, the DDS-1 strain of Lactobacillus acidophilus is the most effective.
As long as your stomach is empty, taking 3 of the Opti-Elite Probiotic can produce amazingly quick relief. To increase the speed with which relief ensues, I chew at least one of the capsules before swallowing so I get some of the powder into my mouth, particularly under my tongue. At times this can get your sinuses to drain within minutes.
Laughed at for years by established scientists, (some of whom used to come into the stores to scoff), the volumes of evidence on the benefits of probiotics for immune function now speak for themselves, and point to the systemic anti-inflammatory effects that are exerted when probiotics bind with receptors in the GI tract, helping among many other effects, to reduce reactivity. They are thought to help shift immunity from more reactive Th2-type to less reactive Th1...this is discussed below. 
Also relevant is the lactic acid that they produce, which helps to promote the proper pH and environment for these health-protecting bacteria to thrive in.
On a side-note, did you know that changing the bacteria that live in your gut, by changing what you eat, and/or supplementing probiotics, can dramatically impact your genetic expression?
Since the dawn of antibiotics in the 1940's, we have spent the last 70 years fighting bad bacteria. It makes sense that if you've got the wrong bacteria residing in your gut they can cause disease! Or if you've got the right ones, they can be a boon to your health, and balance out your immunity!
For a more detailed discussion of the mechanisms at work with probiotics, see the following article.
Related article: What Do Probiotic Supplements Do For Allergies?
2. Optimized Resveratrol
Designed with allergies in mind, this formula has quickly become popular in the springtime for sufferers. It contains the following botanicals: Resveratrol, Quercetin, Nettle root, Grapeseed Extract, Pomegranate, Acai.
Optimized Resveratrol supplies a broad spectrum of antioxidant and anti-inflammatory polyphenols (i.e. flavanols and anthocyanins), shown to specifically decrease production of inflammatory compounds associated with allergy and asthma.  Resveratrol has been specifically shown to decrease human mast cell degranulation, which reduces histamine release. In fact it worked better than the drug it was trialed against.  Quercetin is probably the best known and researched flavanol, not only for inhibition of allergies, asthma, and lowering production of histamine, but also for a huge spectrum of other immune and inflammatory modulating effects as well.  Nettle has also been shown to posess anti-allergy effects by blocking histamine receptors and preventing release of histamine and the associated downstream inflammatory molecules.  The root is rich in sterols that moderate immune balance by keeping in check the above-mentioned TH1/Th2 immune divisions. Grape Seed Extract rich in OPC's, along with Pomegranate and Acai round-out the formula, being an abundant source of polyphenols with various flavones, flavanols, and proanthocyanidins which have been shown to increase tissue and mucosal integrity, and moderate reactivity , , , .
To relieve allergies you can either modify what happens after the immune response has already started, (for example, by decreasing histamine), or alternatively you can prevent the immune response from being mounted in the first place by modifying your reactivity or "tolerance".
Obviously you want the immune system to attack genuine threats, but not to over react to things which would other wise be harmless. For this the immune system requires balance. This means balance between cell-mediated immunity, (loosely classed as Th1), and antibody-mediated immunity, (Th2).
Something I have seen work incredibly well for reducing reactivity in this regard is Ecomer TM. As covered in this past Ecomer article the alkylglerols in Ecomer™ can create a shift in immunity away from the more reactive Th2-type immune responses, (responsible for such conditions as allergies, asthma, excema, hives, etc.), toward less inflammatory cell-mediated immunity, termed Th1. 
Especially for those people who seem to "react to everything", I would recommend 2 capsules 3x per day, for 3 days, then down to 2 morning and 2 evening for a couple of weeks. Afterwards 1 or 2 caps per day will likely suffice.
Other nutrients that can help maintain this type of immunity balance to promote appropriate immune responses are Vitamin D and Vitamin A. (Increased exposure to sunshine is presumably one of the reasons allergies tend to decline in the summer as Vitamin D status improves.) But I have to say that I think that the alkylglycerols in Ecomer TM are a hidden gem when it comes to reducing inflammation and reactivity from an over-active immune system!
4. Vitamins and Minerals
Pantothenic Acid, Vitamin C, and Magnesium
These three nutrients are the classics for seasonal allergies. Both Magnesium and Vitamin C have a stabilizing effect on mast cells, reducing degranulation and release of histamine, and all three have a supportive effect on our adrenal glands, particularly Pantothenic acid.
Supporting adrenal gland function maintains energy production, and one of the main reasons for this is because the adrenals produce several highly anti-inflammatory hormones, such as cortisol, adrenaline, and nor-adrenaline. In turn, reducing inflammation allows energy production to proceed normally, and the mitochondria keeps producing ATP.
We then remain unaffected and continue on with our day, without the inflammatory symptoms that accompany allergies. Particularly pantothenic acid has been popularized for seasonal allergies, and many find it helps in the range of 500-600 mg, one to three times per day. (Keep in mind there is no established upper limit, and pantothenic acid is also widely available in a healthy diet.)
For a noticeable effect from Vitamin C, I would use 2-4000 mg spread throughout the day, but be sure to use a product that contains bioflavonoids for better results. In fact, they may be just as, or more important for this application than the vitamin C itself. This was the rational behind our More Than C formula.
As for Magnesium, I would suggest 400-1000mg per day, but this intake can be limited by bowel tolerance, given magnesium's tendency to cause loose stools or diarrhea. People vary widely in their sensitivity, so you may need to experiment. But increase slowly, unless you are looking forward to spending a lot of time in the washroom that day!
Related article: Maximize Vitamin C Benefits: Key Substances To Achieve This.
5. Opti-Liv Extra and Opti-Colon Cleanse
Clean up your liver, and flush those backed-up bowels
Often regarded as the most important organ when it comes to allergies and excessive reactivity, the liver's detoxification systems, (especially Phase I), can be a huge source of oxidative stress, particularly if it is not working efficiently to properly detoxify and clear toxins.
If the liver is stressed and the "gears are smoking" this obviously can create a lot of obnoxious, inflammatory compounds, which our immune system then responds to creating more inflammation....then reactivity and fatigue ensue.
On top of this, if the bowel is backed-up, what do you think this does to the liver?...puts even more stress on it...which creates more oxidation and inflammation, and round and around we go!
On the other hand, I have counselled people who have experienced immediate reductions in reactivity from either flushing their bowel...(not a big surprise)...or from taking liver support products like Opti Liv or Opti Liv Extra.
These formulas increase production of glutathione, so critical for liver detoxification, and particularly for helping you package-up toxins to be escorted out of the body, (i.e.Phase II Liver detox). The difference between the formulas is that the Extra formula contains additional Alpha-lipoic acid, an extremely versatile antioxidant and Nrf2 activator, plus Selenium, which is central to the function of critical cellular detox and antioxidant enzymes like glutathione peroxidase and superoxide dismutase.
A fermented whey culture of (L+) lactic acid.
Don't let the word "whey" scare you here if you are allergic to dairy. This product can actually improve dairy and other allergies. It is a highly purified extract of lactic acid so important for the health of the probiotic populations of your intestines. But I have to say, the results we have observed with this product go far beyond the typical explanations of its effects being due to promoting proper intestinal pH.
My guess is that it directly sensitizes receptors in the gut, which then exert downstream anti-inflammatory effects....sometimes surprisingly quickly! For example, one of the problems I have not found easy to produce results for is urticaria, or hives.
Hives are caused by a Th2-type immune response that leads to the production of IgE antibodies, which in turn cause mast cells to release histamine.
Recently, we had a woman get relief from her hives within a half an hour after using this product! Obviously, its not going to work like this for everyone, but we have observed at least some improvement in virtually everyone who has tried it.
Approximately 70-80% of the immune tissue in the body is located in the gut. It is very clear that improving gut status by reducing inflammation and/or gut permeability (i.e. a leaky gut that lets undigested particles by), has a very positive impact on an over-reactive immune system.
One of the ways to help accomplish this improvement is with lactic acid-producing probiotics, or just the lactic acid itself, such as is in Molkosan. This product is a good example of where the science to explain exactly why or how something works just hasn't caught-up to the observed, and often unmistakeable results!
So, how do you decide where to start? Some of these nutritional issues such as probiotics or Vitamin D are something that anyone can benefit from. But beyond that, where you start is on the issues that stand-out. If you suspect liver or bowel involvement, start there. If you respond well to botanicals, start with the one of the herbal formulas like Optimized Resveratrol, and if you have broad reactivity, try the Ecomer!
In conclusion, contrary to what some medical models would have us believe, we are not a bunch of segmented compartments. Our systems are all connected, and one effects all the others. This is very apparent when it comes to the liver-gut-immune sytem connection. (As I have always told my clients: the liver and gut are glued together....what affects one, affects the other.) As the Institute for Function Medicine teaches, such is the web-like interconnectivity make-up of our all our systems.
5. Alternative Medicine Review: Quercetin Monograph; Volume 16, Number 2, 1998. Thorne Research 2011. pp.172-194
7. Alternative Medicine Review: Oligomeric Proanthocyanidins (OPC's) Monograph; Volume 8, Number 4, 2003. Thorne Research. pp. 442-450
Disclaimer: The above information is provided for informational purposes only and is not intended to replace the advice of your physician.