I would second the diet change. In the short term try boiled chicken breast with veg and pasta, or similar- thereby reducing the risk of commercial bulking agents being the problem

We sell Kronch salmon oil which helps with skin issues. The other equally good brand is Grizley.

Both are cold pressed with no additives. Just add a squirt to the food- dogs love the taste of it.

For instant relief try a good quality Neem shampoo. Helps with hot spots