my son had the same problem when he was 6months old, after few days in hospital, we went in for further testing, at which time they learned he only has 1 kidney, the other one either never developed or was shrivled up by the kidney reflux he has. I would definitly take him back to the dr, and see if you can get in to see a urologist, we use a great one who is out of OKC but he comes to Tulsa a few times a month. Let me know if you would like his information and i will get it for you. Best of luck to you & your son :)