BAD CRAMPS AFTER SEX!! HELP

It's been about two days after having sex with my partner and I have been having some of the worse & strangest cramps of all. Almost feels like it's on fire. It's just that bad. I'm not sure if it's because we went harder than usual or if it's something completely new. However he did "cum" a little before completely pulling out. So what exactly could this mean? I'm a little scared ?