Need some tips..

So my husband and I have a good sex life and even tried anal like 3 times. He can literally make me cum several times when he’s eating me out and he says he loves to do it to make me feel good. I on the other hand have only ever been with him so he taught me how to give a bj and even though he says he likes it I feel like I don’t do it good enough or long enough because I get tired of my mouth being open in a particular way and sucking. How can I last longer with giving him head? And what other stuff can I do to help him reach his satisfaction since my jaw gets tired? I feel like my mouth is just small and he’s not big, he’s normal size if I had to assume, like I said I’ve only been with him. He doesn’t like me playing with his balls so that’s out the door since I see a lot of girls say they do that to their partners.