What should if I do if I think I have a sinus infection?

Symptoms? Sinusitis can cause many symptoms. The medications including the over the ones address specific symptoms. If this is viral in nature, get rest and stay well hydrated. Over the counter nasal saline spray can help to clear some the secretions. If your not feeling better after a few days, see your doctor.
Meds. If symptoms have been less than a week.. It may just be a cold... Wait it out and treat symptoms. If symptoms longer than a week with facial pain/pressure/ nasal drainage/sore throat... May be a sinus infection... Best to get some antibiotics.