How to relieve sinus pressure and pain?

For the past two years, I've been getting acute sinus pressure on the left side of my face in the fall and winter. It's always right above my top left molars, and it puts so much pressure on those teeth, that I can't bite down or even close my teeth together slightly. It comes without warning and seems like it develops overnight. I've sat in the bathroom with a hot shower running, and taken six over-the-counter sinus decongestant pills. I've recently been laid off of work and have no health insurance, and I don't want to have to go to the physician or ER to get antibiotics. I've never had any sinus drainage when this happens, so I don't can't tell if it's an infection or just pressure. Is there anything else I could do?