It took me until my 30's to realize that I had seasonal allergies... I am sensitive to several things - a couple of tree pollens, grass pollen, dust mites and cats, but really only have symptoms when the trees are blooming, so I'm only really bad for a few weeks out of the year usually.

I'm with Indy - I use allegra and singulair and at the worst times for me I use a nasal spray (flonase) and it works quite well. One of the docs I work with told me singulair does a good job with allergies (but not so much for asthma, which it was actually developed for....) - but only when combined with an anithistimine, so don't bother taking it alone.