What Does It Mean When I Get Weird Rumbly Pain

What does it mean when I get weird rumbly pain spasms in my gut/stomach/lower abdomen right before I have to defecate? I also get hit with a little bit of nausea. It feels like I am about to have diarrhea but the feces come out in small balls-chunks and they sink to the bottom so I know it is not gas related. So what is wrong and how do I fix it? Please and thank you.