My 3 Weeks Puppy Is Vomiting Milk And Water What The Vet Told Me To Give Hes Not Moving Just Lying Down And Crying?

The best thing to do is go straight to the vet or emergency hospital.  Is this "milk" the mothers milk, puppy formula, or regular dairy milk (dogs and cats are lactose intolerant and cannot digest the milk that we drink)  It sounds like it may be far more serious than that though.  If it is a Chihuahua or toy breed it may be its sugar levels are too low and may need IV fluids--puppies need to be fed more times throughout the day and lesser amounts.  If  the puppy is dehydrated (you can tell when you use your thumb & index-finger and hold the back of the skin on the neck and release--the longer the skin stays in place the more dehydrated.  If signs of dehydration, stop milk and start pedialyte or other electrolyte liquid and give a little with a dropper. Take a rectal temperature reading if it is 101 or higher the pup has a fever.  It could be anything & really the vet has the best chance of figuring out what is causing this and the best treatment.