small bare lumps on topside of tail

Been to the vet. I was given cephalexin for a week to see if that would help. Got a recheck appointment in a week. Dr. doesnt think it's ringworm, and would do biopsy to rule out tumor or growths.

Here are pictures of the tail (yellow smear is the nu-stock ointment stains):











Here are shots of the abdomen that looks moist and nasty:





Any ideas of what it could be? should i try to use nu stock still bag balm?

the bumps used to be just 2 flat ones...i successfully treated it with nu-stock...but then the open lesions came back...it seemed like it got crusty and split open and was bleeding...now I see 4-5 bumps that are raised round mounds...there are 2 darker ones that cant be seen in the picture because of the color