It does sound like you need to take a slow approach to food, Patty and Sue gave good suggestions – starting with only a couple ingredients at a time, since he probably has many allergies.
There’s the slight possibility that he’s reacting to environment as well. Maybe try an anti fungal shampoo to see if it helps, and if it’s environmental allergies, possibly trying to give him coconut oil and raw LOCAL honey daily? That seems to have helped my sensitive lab a whole lot when diet alone wasn’t quite cutting it. Plus, the coconut oil helps oral health and makes super soft fur 🙂
