PAINFUL POOPS

Okay so today I woke up with a tiny pain in my stomach. Well I went to do the doo and it was literally the most painful thing in my life. My mom says it's cause I'm constipated but even so it shouldn't hurt THAT bad. I'm talking body shaking, tears, I'm going to puke bad. After about 2 hours of suffering I finally fell asleep and woke up and it was gone but seriously worst pain of my life. The first poop was normal and the second and third, etc was diarrhea. I have the Nexplanon and they weren't this painful before I got it but I don't really associate the pain with the bc. My mom just suggested it. But it literally felt like I had knives in my back and stomach and my vagina and butthole were turning inside out. And I'm not sexually active so the chance of a baby is out. Just wondering if anyone else ever had this kind of pain and if you found out WHY you were having this pain. Any help would be appreciated.