Headaches can be caused by a lot of different things, some of them serious, some of them not, and sometimes doctors can't even pinpoint the cause. If this is happening when he turns his head, it may be a pinched nerve or something of that nature, but you aren't going to be able to tell unless you get him to a doctor. You could also try a chiropractor to see if that helps at all, but the fear of what the doctor will tell you or the tests he has to go in for, won't help the issue to go away and it can only get worse by not dealing with it. Take a deep breath and give the doctor a call so they can take a look. Let us know how you both are doing!