It could be fleas. You can see them best if you put the puppy on his back and look on his underside. But they're easy to miss so going through with a flea comb is a good idea.
It could also be that something is irritating his skin, so try bathing him in a mild puppy shampoo
It could also be that something is irritating his skin, so try bathing him in a mild puppy shampoo