Very intense contraction like feeling after sex

I'm 23 weeks pregnant with a baby boy. Last night hubs and I got busy for the first time in a few weeks. And right after the lower part of my stomach got rock hard and hurt so bad I had to breathe through it like labor! It felt exactly like the early contractions I had when I had my daughter... It lasted about 3 minutes and the feeling hasn't been back since but what the hell?