What is this pain from? My period.. or lactose?

Well, I'm lactose intolerant (mildly), and I ate a little lactose yesterday (not enough to usually bother me though), but I also have my period. I woke up this morning with a sharp, stabbing pain in my lower abdomen. It feels like its exactly in the middle below my belly on. It also went around my backside and well, I guess through the middle of my body, but its mostly in the front now. It almost feels like it would be my bladder, but I had no problem peeing while I had the pain. It did hurt, however, when I took my tampon out, (not when I put another one in). The pain seems to be like, at the bottom of my ? But I've never experienced this with my period before. I've had cramps, and I've had like a pulling, tearing feeling down there, but never a stabbing that seems like its inside if me. Is it from my period, or is it my lower intestines from the bit of lactose I ate yesterday? Should I take Advil or something?