Hope you can get to the bottom of the problem quickly. You might try reading ingredients and try a different protein than what you're presently feeding. Also no corn, wheat, soy or meat by-products.
Many people don't realize how to properly bath a dog. Here's a link to help you understand how to properly bath your boy. Be sure to rinse, rinse and when you think you've rinsed enough, rinse some more. Improper rinsing can cause dandruff. https://www.dpca.org/BreedEd/article...-bathing-a-dog