Have you ever heard of, or tried, using a Neti pot? it is used to flush out the sinus passages to get rid of exess mucus, dust, allergens, etc. I've used it before and it does feel a bit uncomfortable for the first couple times, but it sure beats having a sinus headache. You should be able to get it at a health food store.
i 2nd the neti pot. Sounds like you have some stuff locked up in your sinuses. I feel like a broken record now that i've been irrigating with a neti pot the last few months. I can only say i wish i would have been brave enough to use one 20 yrs ago!