Loose stool 34 weeks pregnant, what does this mean?

On third pregnancy, with all my others I have always been so constipated throughout the pregnancy. Since about 31 weeks I have had loose stool multiple times a day with like those diarrhea cramps. What's the heck, I dont have a tummy virus I feel fine, been eating normal foods nothing in excess amounts. I'm just worried this is a sign of early labor ? Anyone else experiencing this?