Constipation or Pre-labor?

This might be TMI but I was constipated foe almost a week. I finally reached relief about 3 days ago and since then I've been regular. We'll tonight I'm getting some cramping like period cramps. They only last 10-15 seconds and they started around 10:30 so its been 2 1/2 hours. The most I've had is 2 in the last half hour. I'm 31+4 and at my last appointment a week ago an ultrasound revealed that my little girl is head down and sitting low. I'm not sure if these cramps could be from not having a bowel movement since this morning, braxton hicks contractions, or pre labor. What do u guys think?