Mitzi (10 y.o.) had skin problems like you describe for many many years and nothing really helped.
Several weeks ago we switched her to raw food (beef, turkey, chicken, lamb and raw bones, mixed with a little oatmeal,
very little oatmeal) and her skin cleared up finally. I don't know why, it just did and I'm extremly happy.
What helped her before was keeping her hair short, frequent baths with oatmeal shampoo and keeping a shirt on her (that's actually how
PocoMutt designs started... so... something good came out of it. But I sure wish the reason would have been something less painfull for Mitzi and less worrysome for me!!!)
I hope you'll find the right treatment!