Diarrhea Third Trimester

Newly in my third trimester, for the last three days I’ve had cramps which I believe are Braxton hicks and they only last 20 minutes each time. They get better once I drink water. Tonight I’ve had horrible loose stools accompanied with some cramping. I haven’t had diarrhea this entire pregnancy and I’m actually usually constipated. No blood. No mucus plug. No consistent cramping. Should I be worried? Is this normal for this stage of pregnancy? Nervous about preterm labor this is my first baby, please help.