There are also commercial hypoallergenic diets, such as venison, fish, or rabbit and potato that would be suitable if it turns out that your dog
does have food allergy gastritis.
Lastly, there are board certified Internal Medical and/or gastroenterologist veterinary specialists that should be able to help your dog. These specialists can be found at referral veterinary hospitals and Colleges of Veterinary Medicine, check the AVMA website.
Holistic vets may also be able to help.