My Dog Is 6. He Has Diabetes W/insulin Shots And Very Severe Allergies. Is There A Holistic Way Of Treating His Allergies W/out Making Diabetes Worse?

My dog has very severe allergies and diabetes. He is 75 lbs. He has tried every prescription from the vet. They all give him the same thing w/no relief from skin and food allergies. He is bumpy and red and hot and itchy. A bath temporarily relieves the discomfort. He is on a Hills Prescription diet for his diabetes. Is there anything we can do to help him? ANY SUGGESTIONS? We're at our wits end here. And it breaks our hearts to see him like this.