Have you tried a few days on decongestants to get the sinuses drained out a bit? Breathing steam? Hot faceclothes on your sinuses? I remember once having a sinus infection that landed me in the ear/nose/throat doctor's office where he actually vacuumed out my sinuses. Sounds gross, but the relief was phenomenal. (I was pregnant and couldn't take decongestants and was at the end of my rope.)
This is an awful feeling, I can sympathize. Did this infection follow a cold or just pop up on its own?
Last winter I suffered terribly, starting in September, first with difficulty breathing and then with cemented sinuses. The doctor tried numerous antibiotics on me, all with no positive results. When I was still bad in March, I went for allergy testing. It turned out I was deathly allergic to my daughter's guinea pig. It hadn't bothered me during the summer when the house was open, only in the fall when we closed things up. Is there anything new in your environment, have you recently moved, changed jobs, etc?
Good luck and hope you find relief soon.