 [ Symptoms ] can penicillin cure a sinus infection  yesterday i was diagnosed with strep and put on penicillin however i am still struggling with congestion and a bad cough which i think may be sinus related do i need to go back to the doctor for another medication [ Disease ] most infections in the sinuses are viral and not bacterial so penicillin would not likely help in this case i do not know that how you were diagnosed with strep unless you had a lab test to confirm it you may not have strep at all a visual diagnosis is wrong about half the time