Well i just smoke sum pot and it helps to relax you and you dont tend to clench or grind your teeth but does make you want to eat more or sleep

I was advised by my dentist and a pain specialist to use a mouthguard, as it stops you clenching.

Sounds like a mouth guard might help .
It helps with clenching and grinding plus you can put it in whenever you need to.
Speak to you dentist about it

Apparently approx 75% of Fibro sufferers have pain from subconscious jaw clenching. You know, because we need more reasons to feel pain. I didn't realise it was a Fibro thing until I did some research and spoke to my Chiro guy.
I did try some very small contact needles from my massage therapist that sit in the cheek muscles for as long as it takes to release them (I left mine in for a day and a half), but as soon as I removed them the tension and the clenching just came straight back. I don't see how a guard will stop me clenching? Don't they just protect your teeth?

I also tend to clench my jaws when in a lot of pain. I'm prone to severe headaches because of it. I also have TMJ. I had a mouth piece made from dentist so I don't grind my teeth and it's me difficult to clench. Insurance companies typically don't pay for it. But you might try it. It helps some. I started by trying the over the counter mouth pieces first to see if it helped. Walmart sales them pretty cheap. Hope you find a good solution for you. Error and trial to you find what works for you.