TMI ALERT!

So I am 31 weeks pregnant and for most of the day I have had diarrhea and have had contractions on and off. I'm totally freaked out because this never happened with my daughter. I haven't eaten anything out of the ordinary or anything I don't usually eat. I know I am probably overreacting but what usually causes this? It's going on 7hrs of this and I am keep hydrated but I can't stop using this the bathroom every 10-15 mins.