acessorie: For some guys, blow jobs aren't their thing. And for some girls, giving blow jobs just isn't their thing.
Out of the three people I've given head to, there was only one I enjoyed doing it for. Two of them never orgasmed from oral sex and had to finish up another way. They liked it, but viewed it more as foreplay than real sex. And I knew that it wasn't doing a whole lot for them, so I didn't see why I should be putting in all that effort.
The person who made giving head enjoyable for me was someone who really really likes getting head. He's super enthusiastic about it, which makes me want to do it for him. He gives very specific instructions, so that I know I'm doing what he wants. He was very gentle with teaching me how he liked it at first. He views it as a whole sex act, not just foreplay. He doesn't just lie back and take it, he gets involved. He'll put his hand in my hair or play with my breasts. Since we're into kink, he ties me up sometimes. These things make it so much more enjoyable for both of us.
Also, for the jaw hurting thing - give it a rest. When I need a break, I'll lick the shaft, pay some attention to just the head or his balls. Let yourself breath.