may check with your vet for masitis
it is not normal for a 7wk old pup to not be up running and playing i hope they gave you a health guarantee.
If you have not brought him home yet, I would question the breeder and have them pay for a vet check to verify everything is ok. If the breeder is a good one, they too would be concerned why a 7 week old pup isn't running around and playing with litter mates. Get something in writing but I would try to clear it up before you bring the pup home because the breeder might not be willing to help you after.