I have severe sinus pressure and headache...what can i buy otc to help ?

Antihistamines/NSAID: Antihistamines and/or decongestants will help to relieve the sinus pressure and nsaids like iboprofen will help with the headache pain. If this doesn't cut it, it's time to see your doc.

Are you sure Sinus?: If you are sure it is your sinus problems that are causing the headaches, then fine, but are you sure. If you are assuming that since you have pressure in the frontal regions of your head or pressure behind your eyes, this could be part of cervicogenic, neck induced, headaches. The occipital nerve comes out of your neck and travels across the top of your head, into the front and behind the eyes.