Sharp, shooting pains in uterus?

I've been getting very sharp pains in my uterus that almost feels like lightening (it's the only way I can think to describe it) shooting through me in bursts rather than a continuous pain. At first it wasn't so painful, it was more annoying, but now it seems like it's getting worse. Usually it only happens when I'm sleeping or laying down. It happened once while I was at work, and I had to sit down to get it to stop. It lasted about 5 minutes or so, and every time I stood up it would come back. Last night I kept dreaming that I was in pain, and I would wake up and have to roll over on my side in the fetal position to get it to stop (from laying on my back). I'm not positive about this, but I think it only happens when I'm on or around my period, being a week before or after. It's a little scary, and I'm going in for a PAP Smear next week, so I'll tell my doctor about it, but for now I just need to know if anyone else has experienced this before. Also, I'm not pregnant, and I'm taking the birth control called Yasmin, if that helps.