Intense Itching

[IMSprout2]

Hi all- I'm hoping to get some advise on GSD skin sensitivities. My girl started itching at the age of 1, about 1.5 years ago and the vet and I can't seem to find the problem. She has been treated for mites and mange as precautionary to eliminate any doubt. I feed her Fromm 4-star salmon a la veg food. She gets vitamin e, and salmon oil. I have tried wheat germ oil as well. The problem is getting worse. It started out as itching similar to shedding. Then her ears started to thin on the edges. That's when we treated for mange. Lately she has been biting her hind quarters a lot. She is specifically focusing on the area where her back leg meets her belly on both sides. It has been licked raw and her skin is getting dark and inflamed from her biting at it. Any help would be greatly appreciated, I can't imagine how awful it must be. I also tried one bag of wheat free food, she wouldn't eat it.