20 weeks? Just started cramping?

C
Hey guys!
I'm 20 weeks exactly and in the last hour I've started getting sharp fairly painful cramping low down on the right side of my pelvis that radiates through to my back. Anybody else experience this? I'm waiting on a nurse to call me back. I've had a pretty smooth and uneventful pregnancy...so something out of the norm is freaking me out a little :(