What could it be?

Okay, so I'm 35 weeks pregnant. The last few days I'll get a random extremely strong contraction type feeling in my groin/pelvis area. It's so bad I cant even move or anything and I'm almost in tears. It'll last like 3 minutes and go away. And then I'll get a few contractions and I'll be fine for hours. It's happened the last like 3 days. Any idea of what this could be?

(I'm going in next time it happens, just looking to see what you guys think. I know y'all aren't doctors.)