Constant cramping pain in abdomin, 3rd trimester?

So I'm 37w3d and the past 2-3 days I've had this constant cramping/poop pain but in my abdomin. Like when you have bad diarrhea and you get that stomach pain, like that but in my abdomin/lower stomach along with cramps that seem to be getting stronger and stronger. They wake me up and night and keep me from sleeping. I told my doctor and she didn't seem to concerned; I had an appointment today and I'm still not dilated but she did say she can feel the babies head and it's low. Has anyone else experienced this ? And if you have how long after feeling it did it either go away or did you have your baby?