Their is no over the counter medication to treat strep throat. Strep is an infection that requires antibiotic therapy. When you went in for the throat culture they should have given it to you. If the throat culture came back positive and they didnt give you any antibiotics... they will call you to have you get a prescription.
A throat culture is the only way to tell if you are infected with the streptococcal bacteria. Until you know for sure... it is only a sore throat.
Gargling with warm salt water should help... So will sucking on cough drops that can help numb it. Chloraseptic spray helps too.