I have a 2yr old rottweiler mix. I feed her about 4 to 5 cups a day. Took her to the vet they can't find anything wrong. She loves to eat but I can't get her to maintain her weight. Vet notified me she needs to gain about 15 to 20 pounds. I tried eggs,cooked rice, giving her more treats. Nothing is working for her. Since it's winter I'm worried she won't stay warm. She still her happy lovable self. Please help me I'm really concerened about her.