I agree with Chachi, it sounds like you may need an special food. My son's dog has pancreatitis, and they tried to stabilize him for over a year trying all sorts of recommended diets. They had always fed him a healthy diet, with only healthy snacks, so the pancreatitis, was a huge surprise, not brought about by diet, but heredity. He got so skinny, we thought we were going to lose him and they finally tried Iam's Veterinary Formula Intestinal Plus Low-Residue Canned Dog Food, and it really saved his life. That was over 3 years ago, and he hasn't had one attack since. Here's more information on it.
Iams Veterinary Formula Intestinal Plus Low-Residue Canned Dog Food | Free Shipping - Pet360 Pet Parenting Simplified