Pups can come down with Parvo despite having the appropriate preventative vaccine. It is rare but does happen. Any breeder worth their salt would have provided the preventative vaccines on the proper schedule and also had a record thereof for you.
Parvo is bad news. I have had only one pup, a Basset, come down with Parvo. He did not make it. And he was vaccinated properly. Get to a vet ASAP if you have not already. It'll be very tough to save the dog, but it has happened. Good luck!