I'm going to go out of limb here. This may sound a little granola, but it worked for me. When I lived in Texas I had allergy problems for years. A friend told me about a local Whole Foods store that sold local bee pollen. It looked like a bunch a little yellow and greenish grains and contained about every substance known to man that could cause allergies.
He told me that long, long ago the number one way that kings were killed was poisioning. Eventually, some royals started wising up and, starting at a young age, began purposely ingesting very small quantities of known posions. They would start very small and keep gradually upping the dosage until, wallah, they were immune to that posion. He suggested doing the same thing with the bee pollen.
Well, it sounded crazy but I was desperate. I started off swallowing one or two grains of that stuff in the morning. At first it drove me crazy, but after a few days, that dosage would have no effect. Then I'd up it just enough to get a small reaction and do the same cycle all over again. Well, I repeated this enough times to where I could swallow two heaping teaspoons of the stuff and not even sneeze.
I've moved several times since then, and still get the ocassional stuffy nose but I have to admit that my allergies are nowhere near as bad as they used to be. I've probably saved a small fortune not buying so many over the counter medicines and I defintely feel better.
Maybe it's a wacky theory, but it helped me so I thought I'd share it.