I've had a sinus infection for about 2 weeks. how do i know that it is time to go in to the doctor for antibiotics?

Now is good: Most sinus infections are viral, and should improve after a week or so. Sinus pressure and thick, copious, yellow or green secretions that are still present after two weeks, or that make your asthma worse if you have it, should be evaluated by your physician. If you get such symptoms more than 2-3 times per year, you should be evaluated by an allergist-immunologist.

Probably now: If you still have a sinus infection after 2 weeks, you may need antibiotics. Go ahead and get evaluated by a physician.

Sinus Infections: Anytime the symptoms are severe or prolonged is the time to go to your doctor. A common cause of chronic sinus disease is the under-diagnosis and undertreatment of acute sinusitis. The symptoms can even be similar to a cold so don't hesitate to call your doctor or ENT specialist.