Sex and contractions.

Last night my husband and I did the deed, it wasn't rough, and didn't last too long because we haven't had sex in a while. Afterwards, I had some really terrible contractions, radiating along my lower abdomen and into my hips. I tried ignoring them and going to bed, and after what felt like eternity I finally fell asleep. I woke up a half hour ago, had to pee so bad, but now I'm cramping (menstrual like) and my back is killing me. Is this normal? I'm 36 weeks, 100% effaced and 1cm dilated as of the beginning of this week. This has never happened before after sex, not even with my first.