Sorry about the problems you're having. My GSD was diagnosed with severe HD at 6 months old, so I understand how you feel. Was his HD diagnosed with x-ray? That is really the only way you can know for sure. If you're concerned, get x-rays taken. Does he have any trouble walking? The only signs I had with my GSD was that he would periodically just sit down during a walk and whine when he got up after a walk. He never limped or showed any other visible signs.
Pookie, Papillon 4/17/09
Kaiser, GSD 4/14/11