I have a one year old olde English pup. I am concerned about his weight. He is more than just skinny. I am able to see his spine and rib cage. His coat is dingy and he has balding spots. I have tried changing his diet; and I have taken him to the vet. The vet said the balding spot was due to allergies and or a superficial staph infection. He received a cortisone shot and antibiotic pills for the possible staph infection which he has been taking accordingly. Our vet put him on prescribed food. But he is still not doing any better. I am very worried because his litter mate brother has very good muscle tone/ girth, is healthy looking, and his coat is full and shines. I feed both the boys the same amount. Which is a cup and a half of Pure Balance dry food. Well the thin one is now on Iams veterinarian formula;It is a wet canned food. Neither male is neutered. And the thin one's energy levels fluctuate. He can run around the yard but he easily becomes tired. I also noticed he is always excessively thirsty. He will drink and drink and drink until he vomits if given the opportunity. When he was about 14 or 15 weeks he jumped off our front stoop and broke his elbow and shoulder. I don't know if that has anything to do with anything but I want as much information in this thread as possible. These are my babies and I am terrified something is seriously wrong. I know it's isn't anything as simple as worms because the vet has done two stool samples and they have come back clean. Please help me. I feel like enough isn't being done. Thank you for your time and efforts in advance.