I would really look into getting him on Lixotinic - apart from the iron that it contains, it also has a lot of B vitamins and often B vitamins will help stimulate the appetite. You could ask you vet for a B vitamin complex injection, and then get him started on the Lixotinic, I would bet that along with Gastroguard that you would see a big difference in less than a week, but you are probably on at least 2 months before he is really back to being a happy, playful baby. Just my opinion, having been thru it in the past -- I'm really not trying to scare you.
Stacy