A lot of times, breeders will use OTC wormers that simply do not do the trick. You'll need to have your puppy brought into a vet to have him tested for worms so that those particular worms can be treated.
There have been many cases just like yours when owners have lied about their puppies being wormed when unfortunatley they just wanted to get rid of them ASAP.Also some puppies whom seem to be cute and very healthy are not because of poor diets or malnurishment.
If at all possible get this young one checked ASAP.
Good Luck
PawPen