Orgasming without stimulation??

Can someone please explain to me why i had an orgasm without any clitoral or vaginal stimulation?? Me and my bf were just making out and he was also sucking my nipples while i was on top straddling him fully clothed. i felt the urge to pee, but then i realized it was an orgasm and it was really really strong. i don't think i was having any clitoral stimulation or if i was it was very minimal. is it possible to orgasm when only your nipples are being stimulated?