Son wont turn head he favs one side..any help?

My 7week old son will only ley his head on one side when i try to get him to switch sides he will fight it. even if i get him to turn he will just go right back to the other. he doesnt seem to be in pain on the other side just prefers that one side. I talked to the dr about it and she said some babies just fav one side just to keep tryin to get him to switch sides she also suggested a head positioner to keep him from laying his head one way. but he finds it unconfy so i will take it off for him to let him sleep. She saids if he keeps his head one way it will stiffin and he will need physical therapy. I have also tried to make sounds and turn the light to the other side of him so hell look and he turns his eyes but doesnt wnat to turn his eyes. me and the drs have checked to see if he can see and hear and he can thats not the problem. Im worried about this any one have the same problem any one got answers??