I would be happy that the breeder didn't vax him at 6 weeks. That would have been useless as the immunity from the mother would still be in the pups system, deeming the vax worthless, and risky at best. Look at this site for vax'ing protocol, and read about the risks with over vax'ing. Dr-Dodds-ChangingVaccProtocol
Puppies don't regulate their body tems easily, so overheating or chills may happen easily. Puppies also breathe quickly, with shallower patterns than normal, especially when sleeping.
If you are over feeding the pup may have runny stools...Wellness is pretty rich, compared to puppy chow, so be sure you aren't over feeding. I agree, worming may have the stools pudding like too. I'd feed three meals per day and make sure you go by pups weight per portion for now. Until puppy is more active and growing, then adjust according to growth spurts and activity levels.