Big babies will often lose quite a bit of weight after birth. Let him tell you what he wants to eat. Don’t be tempted to wake him for feeds. He will wake when he is hungry. If you wake him and try to feed him when he is not hungry, he will either refuse to take it or bring it all back up for you, as you have found. Despite what it says in the textbooks, babies do not always have the same amount of milk at each feed and do not always wait for four hours. Babies will be hungrier at some feeds than others and cannot tell the time. Just follow him, he will tell you when he is hungry.