Cramping before poop

So I'm on day 30 of my cycle. Usually my periods come on day 28. (I am pretty regular.) Yesterday I had major cramping like worse than when I'm on my period. It was worse when I sat down so I stood up and walked around and it eased it a little but it was still pretty bad. I felt super nauseous and like I was as gonna pass out from the pain. I felt like I had to poop so I went to the bathroom. I sat on the toliet for like 30 minutes in pain and I did finally poop and after that instantly no pain. It happened again later that evening and this morning. Anyone experiencing this? (No period yet.)