how to not get tired giving a blowjob?

so i have a boyfriend of 6 months.. going on 7 months and he's the only person i've had sex with and he's more experienced than me. everytime i give him a blow job, my jaw hurts not even 5 minutes :( so i have to stop like 3 times? but he cums most of the time. i want to be able to give him a blowjob longer without any breaks but my jaw keeps hurting and it's just frustrating sometimes 😭