I agree with Wolfsoul definitely see your vet about this!! It sounds like he's a 'hock-walker'... this has become very, very common in show-bred GSD's. I've met many GSD's that have problems with their hind legs and back and hips because of the way show (AKC, mostly) German Shepherds are bred - for a very exaggerated sloped back and haunches and hocks. It looks striking, but this is the downfall of all of that show breeding ... I met a GSD pup that had been abandoned, he was absolutely *gorgeous* but he couldn't walk on his hocks because they were so grotesquely sloped/exaggerated. He was AKC registered from prominent show lines, and he was dumped by uneducated people who did not want to deal with the vet bills

He probably will need supplements and maybe even physical therapy if it gets worse, OR he could just be going through a clumsy puppy stage ! I HOPE it isn't dysplasia, it would be horrible if such a young pup got it! Bax looks super handsome I hope this is nothing and he gets all better soon.