I know this type of pain! The past two weeks have been absolutely terrible for my jaw, but it's been bothering me for years. I get that same "clicking" sound that 1sweed mentioned, and my jaw has swollen up so much at times that it looks like I just had my wisdom teeth removed. I often feel like I've been stuck smiling nonstop for days, where my muscles get so tight and contracted and I can't seem to do anything to relax them.
The only thing that's given me relief has been a combination of treatments. First, I get a massage. I know that sounds scary to any one who has fibromyalgia, but it helps A LOT. I've found that I have one spot under my right shoulder blade on my back that knots up easily. Whenever my jaw is at its worst, that knot is at its largest. So I have that knot worked out. Then I go for a chiropractic adjustment (I go 3 times a month anyway to keep up progress.) After adjusting the rest of my body he'll adjust my jaw. He's found that it's been slightly out of alignment several times, where the right side is "firing" a half second behind the left side. He doesn't "crack" my jaw like he "cracks" my back, but uses a little pen-like tool on the correct spots on my jaw to stimulate the muscles that hold the jaw in place. It does help. Then, I go for acupuncture. I have needles placed in the appropriate places in jaw. This often helps so much that I don't notice my jaw pain at all for a couple of days, but after those couple of days are up the pain can come roaring back if I don't get the massage and see the chiropractor.
Even after all this my jaw isn't ever 100% normal feeling, just tolerable enough that I'm not thinking about the pain in my jaw 24/7.
My doctor wants me using a mouth guard at night, but a specific kind that only covers the front teeth. The idea is that when we have something on our molars, our reflexes tell us to bite down. So mouth guards that cover all our teeth actually stress jaw muscles even more, even if they protect our teeth. When something is on our front teeth, our reflexes tell us to open our mouths, not bite down. So this guard is supposed to keep my mouth open and relaxed all night. It does do that very well! However, I find that it turns me into a mouth breather and causes dry mouth and sore throats in the morning. It's a catch-22 for me on using it.