Anyone have any suggestions for a dog who has itchy skin?

My rescue cocker spaniel male dog from the south has very itchy skin since we adopted him almost 5 months ago. He is on a grain free diet with no beef or chicken as recommended by the vet and he is also on soft chew salmon oil for dogs. Claritin (also recommended by vet) and Apoquel for dogs did not help. The Apoquel made him so tired and thirsty that he gained 4 lbs in 2 weeks. Anyone have any other suggestions I can try for my dog that works for your dog. I really want to help Chlodo feel more comfortable. There are no rashes or sores any where - just the itch. Above his docked tail under his fur there is some dried flakiness. I tried to spray a solution for itchy skin for dogs, but Chlodo does not like any type of spray on him. Thank you Donna