Babies grow rapidly in the initial year. The shape of head also changes and gradually evens out over next 2 years or so. Don't worry about it. As long as a baby is feeding well, has playful activity, gaining weight and developing normally , he is okay. You may share your concern with your pediatrician at a regular checkup or at the time of vaccination. Most pediatrician will measure the babies head at this time and do a complete examination.