IMO Beneful isn't any better than the cheapest store brand you can find - it just has a prettier package. It also has stool hardners in it which could be part of the problem.
Are you sure the pup was fully weaned? I am just wondering if the pup is actually younger than 7 weeks (which is too young to be gone from mom & littermates yet anyway). I would agree that the pup needs to see a vet before next week if he doesn't start pooping quickly - and if he's not healthy then he should not be getting vaccinations. They could seriously aggravate any problem that he may have.
Livin in a Newfie Drool Zone