Humans are not meant to sleep for 8(or whatever) hours continuously. Our bodies were made to sleep for 2 hours then get up, then sleep for another 2..... However, to do stuff in our daily life, we trained ourselves to sleep for a certain number of hours continuously. When babies are born, they are not aware of how we sleep,etc so they will still function in that way. It will take time for them to be trained and I suggest you should keep patient and help your gf.