Odd Pain During Sex

My SO and I were going at it pretty heavily tonight. I was on my stomach, with my legs in that awesome sleeping position like one is bent and the other is straight. So he put it in and I was like okay sweet and he went deeper and I got this piercing pain like never before in the area right below my appendix area. I never felt this pain in that position before, it was so bad I almost started to cry but I didn't want to ruin the moment so I just moved my body and it was okay. It came back a couple times in some different positions but now It doesn't hurt. Has anyone had this happen or know what it is? I'm kinda freaked out!!