tmi but am freaking out

About 4 hours ago my SO and I had sex. We had to quit half way through because I started bleeding really bad. After turning on the lights the amount of blood was insane. It was everywhere and bright red. I got up to go clean up in the bathroom and it was pouring out of me. It finally slowed down but I'm still bleeding and am having lower back pain and almost period like cramps. The blood is now like a dark red/brown color. I am almost 32 weeks pregnant. Has this happened to anyone else? Suggestions?!