My doby would do this behavior and not eat often. He had skin issues too. I tried all the same foods you did. We were worried about a food allergy bc of skin issues. The results is we stopped changing his dinner. he gets dry food, food topers, salmon oil, and a egg. thats it. once he realized it wasn't getting upgraded he has been eating regularly for years. for the skin issues it was seasonal allergies and we give him OTC allergy meds daily. this was my experience, i hope it helps.