Could I have TMJ?

Yes, it's possible.  In fact, lately I've read about quite a few people who began to have a similar problem in their 20's.  I'd suggest seeing your dentist about it.  You may be grinding your teeth at night without realizing it.  The dentist can make you a night guard that may help correct the problem or at least help keep it from getting any worse. 

3/4's of people experience TMJ pain!  Karen is right, a dentist would be best suited to diagnose and occasionally treat your TMJ! It is something that is fixable with surgery in some cases and in a lot more of the time you can do other things such as a mouth guard to prevent pain and grinding!