Is it normal for a 6 week old puppy to be weak on his front legs and TO GET TIRED FROM WALKING?

my 6 week old puppy falls forward from walking shortly, I want to know if it is normal for him to get tired soon and to limp after a while or can it be a disease in his bones?

The only sure way to find out would be to visit a certified vet and get the puppy checked out.
To be honest, what you have described doesn't sound typical, so I would certainly advise a trip to your vet.

Take care. :]