He may be in the middle stages of metabolic bone disease! Have you been supplementing his food with calcium/vitamin D3? Its really really important that he gets it all thetime because he is growing!! He also need UV light and a basking area of 100 to get his food down and the UV is to absorb the calcium..VERY IMPORTANT! DO IT IMMEDIATELY!! the powder of whatever, if he gets worst send him to a vet to get a calcium injection..good luck!