Vicar,
There's a lot of 'stuff' in the air in Connecticut, I've always suspected. I had constant sinus congestion and allergy-like symptoms my last 6 years there, and I lived there, aside from a stint in NC for 4 years, until I was 25. I was on Sudafed pills for years because if I wasn't, I was constantly congested, pretty much year round. When I finally weaned myself off of the Sudafed, I spent my last few years in CT congested and with minor headaches, but I figured that was better than putting all those drugs in my body.
As soon as I moved to Colorado, a very dry climate, my sinus issues cleared up, congestion went away, and non-stop minor headaches became a thing of the past, and haven't returned. I've developed some allergies to certain types of pollen, but that is fairly short lived in spring and fall.
I'm not saying that you should pack up and move, just that you may want to start taking some additional precautions. Since you seem to have a nagging sinus infection/irritation, you may want to use a filtering mask of some sort until the irritation is completely cleared up so that you can continue your tractor therapy. After that, you may just want to use an inexpensive dust mask - not a bad idea for all of us tractor operators considering the various types of microscopic particles we are subjected to. I don't use them religiously, but when I'm working in extremely dusty conditions, I will put one on, and at the end of the day, I'm appreciative of my good sense in using a mask.