DERMA-IONX which is an oral homeopathic product stimulates the enzyme systems in the body which reduces itching and inflammation, promotes healing of the skin. The supplements I use along with it include probiotics and Omega 3,6,9. I would also suggest that you give your dog only filtered water for drinking and bathing if your water contains chlorine or fluoride. As for diet, if your dog is not allergic to these protein sources you might try a fish or turkey based grain free food since these are considered cooling according to Chinese food therapy. You would want to avoid chicken or lamb which are warming for the skin if it is already too warm. Beef is neutral.
For bathing DEFENDEX shampoo is soothing but effective with essential oils in it.
Please let us know how he does so we can help guide you.