Have to remind myself to relax my jaw, is it TMJ?!!!!!!

I keep catching myself clenching my jaw, no grinding of the teeth just clenching of the jaw. I have no idea why though? I do get stressed a lot due to exams being round the corner and I also suffer with anxiety. But I notice the jaw clenching the most when I'm at home which is where I'm most relaxed and not anxious because I'd say i suffer from social anxiety rather than full blown anxiety. So I don't understand what's causing this! Is it maybe my fillings which I've read I should get removed due to mercury toxicity, but I've had these fillings for years and I've only started to experience jaw clenching for a few months! I also read that jaw clenching can be a sign of parasites? I'm going to do a 10 day juice cleanse next week, I'm hoping this will help!! Thoughts??