Neck muscles

My baby is 10 weeks old and has really good, overall all body strength, but he only keeps his head to one side. He gets frustrated if I try and move his head to the other side and when I do move it, he moves it right back to the side. When sitting him up, it goes to the one side, or he can hold it up straight, but never to the other... When doing tummy time, I can tell if its him rolling over or if its just his head taking him down and rolling. Anyone have a baby that favors a side WAY more than the other? Or know what I can do to help ? He CAN turn his head, but he refuses to much of the time.