4 week puppy not walking on back legs
Hi
You need to have this pup examined by your vet to find out why he's not walking properly.
It could be a spinal, nerve or neurological problem, or he could have a congenital issue or some other condition.
I'm afraid only your veterinarian can make a diagnosis and the sooner you find out what's causing his problems the closer you'll be to helping him overcome them.
Sorry I can't help more but I wish you the very best of luck with your puppy.