Lower abdominal cramps under my stomach & back but only at night. Anyone else?

Karishma
I'm 37wks & 4days pregnant and recently I've been getting these sharp pain/cramps under my stomach which moves to my back. 2 nights now this has been happening also I keep getting the urge to pee/'poop' but wen I go to the toilet nothing happens the pain also gets stronger. Has anyone else experience this? Do you know what it might be?