Last fall I adopted a dog and about a week after he was home he started scratching and chewing his "knee" area.
I did everything I could think of, I took him to the vet, changed his food in case he was allergic to chicken, bathed him in anti-itch shampoo and nothing helped. I read on the internet (can't put anything on the internet that isn't true) that sardines in oil help with dry skin and itch so we gave him one a day. I had a new dog bed for him and I took that away also. I also stopped bathing him and he got more exercise. Don't know which one of these helped, but shortly after I took the dog bed away he stopped itching. Could also have been nerves from the change in being adopted. Just glad it stopped as he was getting bald. Good luck - it sure can be frustrating for you and your dog