I have TMJ and your symptoms sound very similiar. I have had it for 5 years now and there are times when the pain is just unbearable and unpredictable! I have learned ways to cope though....don't chew gum! That's the main thing that I have found to trigger pain and popping. When you sleep, try not to clench your teeth together, if you can. If you do clench, you'll wake up with you jaw hurting. I have found that stress can make my jaw hurt more painfully and more often. Try to limit stress, in which ever ways work best for you. And you're right, it's hard to tell one day from the next when it will hurt. I have found out that if my neck, ear, jaw and head are really hurting, I can use a heating pad for about 20 minutes, and then put something cold on the area and kind of switch off for about an hour, and the pain goes away. Lots of caffine can also trigger pain. I'm not a professional or anything, but maybe if you try to not chew gum or really chewey crunchy things, limit caffine and stress and don't clench your jaw you'll find the pain less frequent. If this is true, it could be TMJ.
Good luck, hope you start to feel better!

oh yes those are symptoms of tmd----you should find a good chiropractor and an good tmj specialist( if you need help i can help you ) and follow lil_scorpio's advice----ive had this for a very long time--i was born with it. you should also do some exercises for your jaw just to keep it open and so that the muscles dont atrophy