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!