The only way to know if it's strep is to get a culture done.
If it's strep, it'll still be positive even after a few days. I suggest getting the "rapid" strep and a culture (when it grows for a couple of days). That way, if it is strep but doesn't improve with treatment, you'll know which antibiotic
to change to -- only the true culture can show you that. Two tests means two swabs though.