I know all dogs are different, and have different energy levels, but small size, itchy skin and missing hair, and not a lot of energy concerns me a bit. Sorry to hear you are frustrated! I would love to see a picture of him.
Did the Benedryl help? My dog had a few times when he was itchy after going to the farm and putting him on Benedryl for a few days really helped. What kind of food is he on?