I would definitely have your dentist check it out. I agree that it sounds like TMJ (tempromandibular joint disorder). If it is TMJ and you don't take care of it, you can end up with a muscle spasm in your jaw. Muscle spams are incredibly painful - I speak from experience.
It can also damage your teeth from grinding/clenching.
It sounds like you might have TMJ. I can't remember what that stands for but it is a common diagnosis for jaw pain related to the joint and the allignment of your jaw and/or teeth. You should go to your dentist to have it checked out.
The problem could also be as simple as a grinding habit. If this is the case, all you need is a mouth guard or treatment to break the habit.
