take him to the vet and tell them to test for parvo virus my dog was about 2 years old and had all his shots and still got it i was told there are two kinds now
I definitely think you should take him to the vet. Vomiting whte foam CAN be a symptom of bloat (which is a serious medical emergency) -since he has had this for 3 days, it doesn't quite sound like bloat, as bloat comes on very suddenly and can literally kill within the hour!
But it's probably more likely he has a bad tummy upset. Drinking a lot and peeing a lot could also be a symptom of a few problems, from kidney troubles to diabetes, and a number of other things. It might be a wise move to get his bloodwork done, to be on the safe side. Many problems, if caught early can be treated successfully.