Probiotics would be my first step. He has an internal imbalance. Second, coconut oil and fish oil. If you don't heal the inside, then you won't heal the outside.
Look up Candida yeast overgrowth and dogs and see if the symptoms fit.
Seger vom Sitz von der Hose
Forever loved and missed.....Banshee
~The strength of one's opinion should not exceed their knowledge on the matter~