Hi Ducky, I had TMJ as a pre-teen and my jaw used to lock
open when laughing or yawning. It was so awful! After having braces, that ended. In college I had problems with my jaw, neck, and migraines. Again, went to the dentist, it was acting up. I got a splint (or night guard it is sometimes called.) They make you wear it for a few weeks full time then you just wear it at night. It worked wonders!!!!
If you have dental insurance, it will hopefully be covered. They are expensive otherwies. I rarely wear mine now unless I start having problems (usually when I'm either very stressed or very sick) and then it will go away after a while. Apparently I am a clencher when I sleep. My dentist's office laughs at me as I'm the only person they've ever seen chew/grind holes in their splint.
My husband had a lot of the same complaints you have. One day he was yawning and hurt his jaw and then he couldn't chew w/o pain, etc. He got a splint and wore it at night for quite a while until he was better. He never wear his anymore.
Good luck. **