I know it's been a while...
I don't know if you are still active on here or if you will even see this. My dog has the exact sores your dog had. She is a 7 month old Pitbull. She started with just a couple of sores on her neck and shoulder, then when one went away (seemingly) a ton spread over her shoulder, and now down her back to her hips. She has red spots on her belly, and the same irritation on her elbows and the heels on her hind legs. I took her to the vet today and got the same antibiotic you did. Cephalexin. I have the paste though, and instructions to give her 4milligrams a day for 15 days. I have given her one dose so far so obviously we haven't seen any results. I was owndering though how your dog ended up. If your dog recovered and the medicine worked? I am worried about my little girl and am terrified that this isn't going to solve our problem. I really just don't want to be one of those people who is in and out of the vet constantly with their dog suffering through trial and error of medications. If you could help me at all, I would really really appreciate it!