I have the worst allergies of anyone I know.
It used to be just congestion and tons of sneezes. Over the last month, my nose now runs whenever it feels like it, with no warning whatsoever.
In public, I find a distraction and get lost in it. The allergy seems to disappear. A few good blows into a tissue seem to help for a longer time than just incessantly swabbing at my nose.
At home, I am affectionately known as "The Snot Monster" because basically I shove a Kleenex artfully up each nostril and leave it lodged there. After an unknown period of time, the runny stuff quits.
I've been hoping someone would mention allergies on the boards since Asperger's seems to affect just about every other aspect of my life, why not my annoying eternal sinus issues as well?
Also, back when I could afford it, allergy shots worked wonders. You may look into that, if you haven't already.
I avoid Benedryl these days. I apparently developed a resistance to it, since I was taking up to six capsules every morning before class and still sneezing my head off by the time class started. I could barely keep my eyes open, but I was still sneezing away.
Good luck. I feel your misery...
If you find a fix, let me know.