Giving head

I have a new boyfriend and he’s significantly bigger than anyone I’ve ever had, I’ve given blowjobs before but I seem to be struggling with someone his size :( my teeth keep accidentally scraping against him and my jaw gets so tired a few minutes in but I rlly want to please him as I’m his first sexual experience!

I need tips on how to give head to a guy with a big dick because I can’t keep disappointing myself any longer😂😂