It probably comes from clenching your teeth or grinding them. Even tho you may not do it during the day, you probably do it in your sleep, or just don't realize it. Try having someone stop you during the day to remind you to check about what you are doing with your jaw. My husband does this for me..."Sweetie, your jaw is set!" and then I will relax it, having not even realized I was doing it.

Having a set or clenched jaw or all or even part of the day is going to cause a lot of what you are feeling.