Weird pain

Orc • You and me baby ain`t nothing but mammals, So let`s do it like they do on the discovery cha
So last night my fiancée and I had sex, everything was normal until the end, it felt like out of no where my uterus started contracting. It hurt like hell, thankfully we had both finished because I made him pull out immediately and rushed to the bathroom. It felt so weird, I almost wouldn't call it pain, more likely call it an uncomfortable feeling. Almost like a crap during menstration but not quite as sharp.
Has anyone else experienced this?
Any suggestions on what it was?