Vomiting in dogs after the delivery of puppies can be due to eating of too much placentas. If dogs eat 1 or 2 placentas then OK, otherwise it can cause stomach upset. Vomiting in dogs is also seen after whelping when owners feed them too much. Anyhow, if vomiting in dogs after delivery of puppies is accompanied by weakness, lethargy, loss of appetite, diarrhea etc then it is not normal. A visit to vet is necessary.