Used antibiotic for sore throat when it wasn't prescribed should i be worried?

Possibly: It is better to see a dr. And get the throat swabbed to determine what kind of bacteria or other infection, if at all, you are suffering. To take the antibiotic may do nothing, help or mask what you really have. Don't take chances.

Resistance: Infections are either viral or bacterial and need to be properly diagnosed to get treated. Antibiotics are used only for bacterial infections that need them. The overuse of antibiotics can cause resultant resistance in treatment, so it is important to get properly diagnosed before taking meds.