While riding sit as straight as you can. Then put one hand behind your back and continue to pedal. This will bring much relief to you.

Being a seasoned cyclist there is not much pain I haven't endured. The neck pain may be coming because you have a bad fit for a bike. Check it out. Are your handlebars and seat syncronized. Are your feet and knees in the right position. You can do this check with a pendulum string and weight on the end of it.