Severe pain during sex, 26 weeks

B
I'll be 26 weeks tomorrow. I was having sex with my husband in the shower, and all of a sudden I got a super bad pain in the right side of my stomach. It was so bad I just kinda fell down onto my knees and stayed there for a while. It's been about 20 minutes. It still hurts, just not as bad. 
I did notice that I had Braxton hicks at the time. My whole stomach was super tight. 
Any idea what this is? It hurt so bad. Like someone was stabbing me.