Sore Jaws When giving Bj's?

Does anyone else suffer from this? I have tight jaws & I try doing stretches to loosen them up but it doesn't help much. Neither does the fact that my boyfriend is pretty big around. My doctor says they're tight because I unconsciously clench my jaws. Because of this I don't like giving blow jobs because I can't do it for a long time & I feel bad that I can't finish him off. Even when we have sex & he pulls out just before he comes so I can finish sucking him off that way, he usually still ends up lasting longer than I can suck. My boyfriend's stamina can waaaaaay outlast my ability to suck him off before the pain becomes too distracting. Lol. Does anyone have any tips for making blowjobs easier on the person giving them?