I've 13 week pup & I've noticed that he walks weird. He really waggles he back end in a sort of swinging action. Must admit I hadn't noticed, as he's always beside me when I walk him. It was only apparent when my sister pointed it out it to me. & @ puppy training last night none of the others walked like this. I may just being paranoid! Is it maybe just because he's growing?

Is he pacing?

Some dogs, including puppies, often pace ie walk like a camel both left legs forward then both right legs forward, this makes their movement look awful, rather than left foreleg and right hind leg forward and vice versa.

Dogs often do this when they are tired or if they are walking to keep at the same speed as the handler.

Hes probably pacing, moving  the two legs on the same side forward then the two on the other, it gives them a rolling movement
snap tohme/

I don't know if he does this a such will have to watch him again. If you watch him from the front his movement looks normall. It's just from behind. His back legs have a differnt movement to the front. He doesn't do the trotting action likes his siblings. I'm not sure if it's his hips? He some simes looks like he's going to go to toilet.