[pugmomsandy]

You can do an elimination diet. Try a single protein and single carb for 2 weeks and check for reactions. Example fish and sweet potato. Or fish and quinoa (gluten free). Be sure no treats are given unless it’s the single protein or carb. You can add in a vit/mineral supplement later as a dog can have a reaction to any ingredient including supplements and you wouldn’t know if it was the food or supplement.

You can google more on elimination diets as there are probably some variations.