Usually for me such pain is all about how much I have to lift my head to see down the road. If you are having to crane your neck to do the same, then check that your helmet isn't blocking your view down the road. If you look up with your eyes the less of your helmet that is blocking your view the better... at least for your neck. So see if your helmet has a way to adjust it's tilt so the front of it is higher on your forehead. If your helmet has a removable visor, then try a few rides with the visor removed.

It might also be that you have a bad posture on your bike. Don't have a very rounded back. It should be straight or nearly straight. Could be that your bars are too wide and you are bracing yourself too much and your shoulders are bearing all the brunt of the road forces and your shoulder and neck muscles are complaining about that.