Giving head

Any advice on how to give really good head? I used to be good at it and he would finish every time. But since I got braces (I'm 19) and the ortho is making my overbite worse, my jaw gets too sore and I can't finish. It's really been putting weight on my shoulders because I feel like I should be able to do this little thing for him like I used to. Plus having braces has made the space in my mouth for him smaller. Sorry if it's tmi I just need advice.