There is a long list of reasons why your puppy may be vomiting frequently but there's a chance the puppy is just eating to fast which you can confirm by observation. If this isn't the problem, consult a vet.
There are different reasons for a puppy to vomit. Sometimes the vomitting may be caused by having some undigested food. There is a possibility that there may be some diseases such as flues are associated with the puppy.