Lyme can cause TMJ symptoms. I've had lots of trouble with this. My jaw got stuck a few times in college which scared me, and then I started wearing mouth guards.
You can get a mouthguard to help alleviate some of the clenching. Start with a sports one or something from a chiropractor that you can put in hot water, form, and wear at night and at times during the day when you tend to clench. If you grind through it, you'll need to get something stronger made by a dentist.
If the plastic is bothersome, soak it in a cup of water with a drop of tea tree oil, and then in water with some peroxide.