Y is my sons head still coned?

my son is almost 2 months old and his head is still severely coned still and will not lay flat on the back of his head.. and time he is flat on his back his head will only go to one side or the other never flat on the back of his head... what could this mean..and y hasnt his cone gone down? we went to his 6 week check up last week and doctor didnt say anything.