pain that feels like menstral cramps...???

ak3627

After I showered this morning, I went to the bathroom because I felt like I was going to have a BM.  After having one successfully, I buckled over with what felt like the worst case of menstral cramps...they put me on the couch for over 40 mins of constant pain.  They finally subsided...but boy did I get freaked out a bit.  Any suggestions on what this may have been?  I am 33 weeks and a first time mom.  Any ideas would be greatly appreciated.  Thanks.