How common is it to cramp in the 2nd trimester? I'm 18 weeks tomorrow and today I had medium cramps that would last for 30 minutes. It didn't feel like stretching, they just hurt. All I could find on google was about round ligament pain but it said I would feel a sharp pain when I moved. These cramps would come & go and lasted for awhile also they hurt my lower back. What's going on?