I agree with Judi, a vet visit would be the first thing I would do.
It seems to me you may have not chosen a great breeder if she was letting you pick out your own pup.
Most breeders also have in their contracts that you take the new pup to your own vet within 48 hrs of purchase. You did sign a contract???
Fingers crossed that he is healthy and just overwhelmed by the changes in his life.
Gina