Definitely see a paediatrician - what you are describing is not normal and isprobably a consequence of his sleeping position. It's something you should get sorted out now, before his skull bones fuse, as the other girls have pointed out. Don't let your GP fob you off, insist on an appointent with a paediatrician. Otherwise, as the others have suggested, investigate anything involving the neck - parfiaitric chriopractice or osteopathy is a good ide.