I've had a lot of pain and clicking in my jaw for months now and my dentist said it's probably because I clench my teeth. I have never been conscious of myself doing it but I have got a hospital appointment on Monday to see about it. My dentist thinks i'll get a mouth guard for it, like a lot of people have already mentioned.
If you decide to see someone about it, go to the dentist, not the doctors. I went to the doctor and it was a waste of time as it's a dental matter seemingly.