First, welcome to YT
. I am sure you will enjoy reading and writing the posts here.
So sorry your baby is so itchy and uncomfortable. At least you have the ear issue diagnosed and treated. As for the general body itching, you say you bathed him in flea and tick shampoo. However it is possible that it may not be doing a good job on the fleas etc. Do you have either topical or pill forms of flea and tick preventives where you live? In the US dogs are treated regularly with the preventives and we do not usually depend on the shampoos.
As others have said, you really need to have a vet diagnose the cause of the itching before you can treat it. The vet will prescribe meds that may ease the hot spot areas. I do not know that it is safe to use human meds for dogs, especially when the cause of the problem is unknown.
It could be that the dog is allergic to the shampoos, the environment or even the food ?
Hope your baby gets diagnosed and treated soon as he must feel very miserable.