There are those who swear by the locally produced raw honey here in the Birmingham, AL area, and frankly, it makes sense to me though I've never tried it. Depending on the year, I've seen the pollen so bad that the air looked like it was yellow when looking from a high point down into the valleys around here. We were fortunate this year in that it rained often enough to wash the worst of it away before it became a real problem, though highly allergic people have problems, regardless.
Sneezing in a full face helmet is not a good thing...that's why I wear a modular/flip face Nolan...I can at least flip it up, hold my nose, and let the blast go out through my mouth. Actually, a FF helmet may help keep some of the airborn particles from hitting you squared in the face...
It is a serious issue while riding a bike. Try the honey...it makes sense that by ingesting a tablespoon or so of local honey each day, you are allowing your body to build up a resistance to local pollen effects. The Clariton works well also. Short of that, see a specialist, get tested, and get the needed shots.