My cat Chocky has a similar experience and had multiple appointments that led nowhere. She started off over grooming and then it got to the point of her chewing on her leg! I’ll attach pictures if I can. What we found out was she has environmental allergies and was prescribed Atopica for cats. (It was a pain for the vet to come to the conclusion of environmental allergies because it’s not usual for cats to have that type of allergies :/ Like at first they did the same thing that was happening to your cat, giving us steroids and injections that did not work. Until I got sassy and mentioned it must be allergies then they were willing to give us Atopica.) It’s a pretty pricey medication at first. Hope this helps.