When I was about seven months pregnant, I started having bad cramps. I went when into the hospital and it turned out that I had a bacterial infection and it was causing contractions. The doctor gave me some antibiotics and everything was fine. It could also just be Braxton Hicks. When I had them it was more of a crampy feel.
phone your OB or midwife or go to the hospital as it could be a sign of pre term labour.