This is long but perhaps parts might be helpful, especially considering it's care provided by a veterinarian dermatologist and not the internet!
Not long after I got Jack, he began scratching half the day, his hair began thinning and his skin was beet red with scabs. Initially, I took the Apoquel and Royal Canin approach, expensive with a life-long dependency on products that were certainly not a cure. There isn't much in the standard veterinarian's tool bag for itching, so I went to a holistic vet and while her tinctures and such may have helped, he was too far along in his condition. I found the veterinarian dermatologist and finally Jack's improvement began. He had yeast (he smelled yeasty) and skin infections, determined by skin tests analyzed right there in the office. He was put on antibiotics, Cytopoint, Simparico TRIO, and Douxos3 shampoo twice a week. Once the fires were quelled, I opted for a long term, less drug dependent plan of allergy drops, which was a concoction she formulated in the office of most everything he was allergic to, mostly mites (through the roof allergic) and grasses. He receives the drops twice a day orally and providing I keep up with them, especially in the summer, that is enough to keep him from scratching. In the winter, I have actually stopped the drops altogether. If I've been negligent with the drops, he will have to get a Cytopoint injection ASAP in order to stay ahead of the itching, which if the scratching becomes bad enough, the allergy drops might not rescue him and he would have to start at the beginning again. The allergy product is not cheap but it goes a long way and is benign, my preference. I have also continued monthly shampoos with the expensive Douxos3 and the Simparico TRIO chewables. Additionally, he has a raw diet of 80% meat 20% vegetables with a little canned thrown in, a diet which the vet wanted me to continue. At the beginning she also wondered if he was allergic to his food, which was primarily beef with occasional chicken, lamb and pork, suggesting I try rabbit and KANGAROO!!, that is, meat from animals that weren't feathered or hooved. Fat chance I was ordering exotic meats from around the globe! His meals are from a book titled Real Food for Healthy Dogs and Cats, by Dr. Karen Becker. Allergy drops might not work for every dog, though I had monthly allergy shots given to another dog in the early 90's and they too were successful, so much so I was able to stop the shots altogether. Jack will never experience that though, after having been on allergy drops for 3 years and an occasional Cytopoint injection. Jack also has the genetics of three working dogs and he has anxiety issues and is noise reactive, not uncommon in those breeds and that psychology could also be contributing to his scratching.