mouth guards stop working in the long run for some people (trust me on this).
Your dentist seems to not care about your situation. Because usually in terms of TMJ or any form of jaw issues, it is him that should offer you solutions or advise you to see a specialist. I
I kept on having issues on my right jaw. And kept on seeing the family doctor. In my case, I actually popped my right jaw 10yrs from band class (playing instrument). It was lose (not aligned) but Dr said it'll adjust. It come back here and there but it just "pops".
But now, it is excruciating pain and its unbearable (especially in the morning) and the reason is because the jaw isn't moving, thus when I wake up first thing it hurts for the longest time and I don't even wanna talk. Then finally seeing my Dr for so many times, he then recommended me to go to dentist (geezus...)