Yes, I do believe this thick mucus will resolve spontaneously, provided you take the penicillin as directed, daily for the full 10 days. Even after the strep have been eradicated by the penicillin, the inflammation the strep caused may continue for a while. This is nothing to worry about, provided that the soreness does not return. The mucus is mostly a nuisance, not an indication of the return of infection.