Sometimes it's just a case of puppy eats and then runs around. If it continues, it will irritate the esophagus and you will see blood in it.
There are many reasons for a dog to vomit regularly. Some are anatomical, some are disease process/parasites and sometimes it is environment. Parasites are hard to eradicate in a litter environment because as fast as the breeder deworms, they lick each other and reinfect themselves. Roundworms, the usual culprit, are often dormantly stationed in the mom until she becomes pregnant. This activates them and they are passed to the fetuses during development. That is why most puppies are born with them. If everything else is okay on bloodwork and examination, you might want to deworm now and 10 days later to make sure the little monsters are gone.