Im sorry to hear about your puppy, he'll need to see a vet to get some test done.
my 6 month puppy is in trouble , it cant walk by the support of his rear leg,his rear leg doesnt have that much of power to walk,it was happend recently,when his tail was wounded,on that time he was biting his tail,but know the wound is cured but,he lost his rear leg,difficultly he can walk,but not like other dog. before he was so fit to walk, run n all.but recently he got a problem. i showed that to the vet,but he raised his hand,know iam helpless.can u people help me to my puppy.....?