Regarding allergies, your best bet is to go to a board certified Veterinary Dermatologist (asap) for exam/diagnosis/treatment.
Continue to work closely with your General Practice Vet regarding GI issues.
It’s not the chicken (just my opinion based on my experience with a allergy dog)
This is a good weight management food, run it by your vet https://www.gofromm.com/fromm-family-weight-management-gold-food-for-dogs
Add water to all dry food, and use wet/canned food when possible.
PS: They (dogs) all act like they are starving, no matter how much you feed them. They are scavengers. Don’t be fooled đ
