I have it too, nothing seemed to help...I was on flexeril and naproxen and vicodin, ice and heat didn't really help either. I had to go to physical therapy and have them stretch my jaw and un-spaz the muscles of my neck, everything had seized up so bad only physical therapy and muscle manipulation could help.
I have to do these exercises now, you put your tongue against the top of your mouth and open your jaw a few times, that keeps my jaw from getting useless again, and I have to rub my neck and shoulder a couple times a day too. I still get the popping and clicking and pain, but at least I can eat again. I know that probably doesn't sound too awesome but it's better than being in constant agony from the pain...maybe if you can still use your jaw to some degree the stretching stuff can help you.
Are the CVS night guards the ones that you buy OTC at the drug store? If so, I tried that once, but had great difficulty forming it properly and just couldn't get it to fight right----so it was $25 down the drain. Fortunately, my dentist made a soft night guard for me and I think it cost about $150. I believe that the costly ones ($500) are the hard ones made specially by an orthodontist.