Help! I don't know what's happening.

I just went to the bathroom and the toilet broke so I was bending over trying to fix it and when I stood back up, I got the worst pain in my lower back and in my stomach and my stomach got really tight. I was at the point of crying and I had to pause. It lasted for about a minute but now my back is killing me and stomach is still tight. it hasn't been all morning. What should I do? I'm 31 weeks today. Ftm