Yeah, he's hitting your G-spot.
It all depends on what position you're doing it in and which way his penis curves. if it curves slightly upward, missionary position will do the trick and he will hit your G-spot. if it curves down, he'll probably hit it from the back. [no pun intended]
if you don't want him to hit your g-spot, then avoid positions that will make this happen.
I actually find the peeing feeling quite pleasurable because it makes me tighten my muscles as a reflex, i guess, so that i won't pee. sooner or later, you will reach orgasm and it will all be worth it, so have fun