Will my puppy Dillon's sensitive stomach get any better?

My puppy Dillon is 5 months old. He can only eat Butchers meat. If he eats anything else he gets bad poops. It's pretty disgusting. He can't eat anything different. My other dog used to eat Bakers but Dillon cant manage that so they both eat butchers. Dillon cant even keep down dog biscuits. Why is this? Will it get better?