Dog had hair loss and skin is black on lower back by tail ?

This same thing happened to my mothers rescue German Shepard she would literally chew her lower back until it bled. She took her to the vet, tried almost every food, tried many medications and nothing worked. Ended having to put her down last year because of age and her arthritis got soooo bad she couldn’t stand up. Hope you find a solution.

He needs to see a Vet.  Next time you have an itch, put a collar on yourself to keep yourself from scratching.

You sound like an a$$.

It looks to me like it is an allergy to grains in the dog food you are feeding him. Switch to a grain free dog food & I bet it goes away.

Another thought would be Demodex mange caused by a mite that burrows under the skin but that usually starts on the face or legs.

For allergies to dog food with grains just switch to a dog food with no grains. It is usually the wheat. No shampoos are going to help this. It may soothe it but it won't help it.

If it were to be the mange, it takes a while to get a handle on it.

Mites (mange of which there are two).   Your vet would do a skin scrape to identify what's going on.

A vet certainly would

Kudos to you for rescuing this poor neglected baby.

The antifungal is a great start, to continue you need the help of a vet.

This is probably the result of poor nutrition in additional to other physical factors.

There are two kinds of mange, bacterial and sarcoptic (mites) I think this might be one of them.  VERY treatable and you’ll see fast results - but you need to see a vet.

is it mange ............................

Could be mange. Get this poor dog to a vet. I hope you reported your friends that were neglecting him?

Yes, someone knows what it might be. That person is a veterinarian. Vet-er-in-ar-i-an.