hi -
sounds like emerging torticollis. I would recommend talking to the doctor for a referral to physical therapy. the therapist will give you specific stretches to complete at home. if you catch it early it's NOT a big a deal, but if you wait and it continues untreated/becomes worse it can lead to facial asymmetries and other issues.
Also as an FYI where i work they have a specific protocol they use based on evidence/research. one thing they typically recommend is an eye exam since torticollis can be caused by visual issues.
In the mean time rotate him in the crib so if he wants to look out of the crib he needs to turn his head to the non preferred side and place toys on his non preferred side.
here is some additional info: http://www.torticolliskids.org/
hope that helps! if you have any other questions feel free to send me a message.
PS yes reflux can be a cause too so it sould be ruled out. KUDDOS to A. for telling you to meantion to the doctor (if he/she suggests it) not to "wait and see" she is correct - the earlier you get him in the better :)