Have you taken him to a vet? I always worry when one of our dogs isn't him or herself.
Sometimes with young dogs, their joints can pop in and out. That stops when they get older.
Have you tried putting gravy on his food. Our Siberian husky went through a phase where she lost about four pounds - a lot for a dog. Dogs can be manipulative.
You have to do what you think is right but personally, I would take him to a vet.
Hope "your boy" is alright.
lonewolf
I vote: VET! VET! VET! VET!
it sounds like panosetisis, German shepherds get this. That said, I would get hi and elbow x-rays, hips to see if there is dysplasia and elbows to chech for a variety of elbow problems. If it keeps up moving from leg to leg, not always the same I would guess pano. Such a large breed should not be on a super high protein dog food contrary to what the manufacturers want to sell you. what do you feed and what is the protein?