My 13 year old Dachshund is on a raw food diet and continues to gain weight.?

We adopted our dachshund when he was 11 and switched him to a raw food diet and food supplements. He was barely walking when we got him. Within a couple weeks, he was running and we began exercising him everyday. He gets a rounded tablespoon of raw meat and several raw veggies twice a day and yet he continues to gain weight. He gets one tiny treat a day and no table scraps. His health is suffering because of his weight and I do not know what to do.