Belly rash?

With him being so clearly distressed and the current options not offering relief, I'd be seeking a second opinion from another vet or at least insisting on a more thorough investigation from your current vet - depends of if your vet was more "wait and see if it gets better" or totally dismissive of your concerns. With having such a rough start in life, I'd at least want a skin scrape done of the affected area to make sure there's no further mite activity and tests to rule out the possibility of a skin infection (bacterial, fungal, etc). Without knowing what's causing the problem, it's going to be very hard to get it under control at home. Good luck, and let us know how things go with the little guy!

Thank you! The vet wasnt dismissive, but they did a scraping at his first round of shots. She said it was probably just still healing from mites. We have washed and washed his bedding, but I think I may have to get more stern. I just feel bad and trying to find relief. The baths really help, but I cant give home more than 1 a week since he has more natural hair.

Yeah, I'd give the vet a call and explain that it's still a problem, especially if it's been a week or more with no signs of improvement. Sometimes irritation from one thing - like the mites - can turn into another problem - like a bacterial infection due to the skin being damaged from scratching. Make sure you're using free and clear (undyed, unscented, usually marketed as hypoallergenic or allergy friendly) detergent when you wash his bedding in the meantime, because that can sometimes be irritating on damaged skin even in dogs who aren't typically allergic.

I would ask your vet about the possibility of a staph infection. It's a common occurrence in puppies that have had a compromised immune system for whatever reason.

I'm with DaySleeper. There are veterinary dermatologists, and that's where I'd go next. My experience has been when a general practitioner vet can't figure out what's going on a specialist is worth it.

Poor baby is lucky to have you, and I hope you get things cleared up soon. I don't think I'd be considering anything that sorry excuse for a breeder did going forward.