Worrisome vs normal cramps

I'm 8w3d and for the last two hours I've had cramps really low in my pelvis. Feels like my uterus. I've had it off and on but it's never lasted this long. Initially I thought maybe it's stretching of the uterus, which is normal but it's been two hours! It started in the middle and now it's moved towards the right and sort of into my groin. 
What is normal cramps and what is not??