help?

Last night while me and my SO had sex I got an intense cramp in my lower stomach (kind of like when you eat and then right after go and jump on the tramp kind of pain) so we stopped for a second I was thinking it was round ligament pain because that's what it felt like- but then after my lower back hurt- so so bad. And when I'd get up it was a lot of pressure making me feel like I had to poop. Should I be worried? I'm a FTM and am not sure what's normal and what's not, because I'm fine today...