I apologize for the vagueness of my answer, but the causes are too expansive to review them all. With that being said, a few examples could be your sleep position, your pillow, your mattress, your medical health history, and so on and so on. The best advice is to go to a chiropractor. Ask colleagues, family, friends, or Google your area. Ready the reviews and make your best informed decision. You should be comfortable with the path you have chosen. I hope this helps.
Dr. Joel D. Duchon
All the best,