Sorry, didn't mean to scare you. In fact, if the swelling is going down, there's nothing to worry about, anyway -- you're on the right track.
Background: The lab that my then-doctor (a naturopath) used (when I kept having strep throat) would report a result back to the doctor to following day, and it would invariably come back negative. But they'd let the culture run for... longer. I can't say how much longer. Another day? A full day? A couple more days? Whatever. Ultimately, it was the second one that always showed positive for strep, not the first one.