I am allergic to everything typical, but didn't develop the allergies until I was 18 or so. One spring I had a sinus infection that lasted for almost 6 months and finally my shitty doctor recommended I see an allergist. Lo and behold, I had allergies (duh). So I started getting shots for about a year or so and that helped a ton. Have yet to have any lengthy bouts with sinus infections since then, and its been about 7 years or so