Hello! I have a similar situation, though my maggie is still in an irritated state. We have been to the vet twice, first time we were given an antibacterial shampoo. I used it every other day on the area per my vet. That didnt really help, and the bothersome area only grew. The problem is on the side of her neck, she is very itchy and has lost a lot of her fur. She has scabs from scratching so much (and it did get infected despite the shampoo) - when I noticed the infection we were given Benadryl, a steroid, and an antibiotic (all in pill form). We just finished those up after about 12 days. The area is still bothering her (itchy, blisters, raw skin), and I have noticed bumps (like very large raised bug bites) with black scabs on them. This sounded like what you had previously. She has some black patches appearing on her skin too - these were not there before. Maggie is 8 years old, well groomed, really an indoor dog aside from our walks (we live in a city), and never had skin issues while we have owned her (she was adopted at 4). I think i will look into a vet derma too...i just feel so bad for her, it looks very painful
I will try to attach a pic...