Constipation Pain

My hubby and I had a date night tonight and while at the theatre I began to experience excruciating cramps in my lower abdomen. It also felt like a grapefruit was trying to make its way out of my colon. Sooo painful. At first I thought it might be the beginnings of labour/contractions but the stabbing pain subsides within 30 mins. Still no bowel movement and I'm terrified I'll go into labour constipated (I'm 39 wks today). I'm taking Metamucil and drinking plenty of water to try to move things along. I hope the poo Gods will send me some relief soon!