I'm not yelling either. My shihtzu had a HORRIBLE problem break out from using a Hartz flea collar. After just a few days she had open, oozing sores on her neck. We threw it in the trash, took her to the vet (gosh, this was probably 15 years ago, don't remember what they did) and have never bought a Hartz product since. Or used a flea collar.
Don't be hard on yourself. We've all used products we wished we hadn't. And I don't think there is anything wrong with a wait and see attitude with minor issues. You've waited and you've seen it get worse. Now's the time for the vet.
Good luck!!!!!