Open Question: What does dark hard stools covered with thick green mucus mean?

I just got out of the hospital yesterday for a hiatal hernia, but I have been getting severe lower abdominal pain as well as lower back pain that's been going on for 4 months now and just yesterday started getting some thick green mucous over my stools as well as black coffee ground looking pieces in my stools (sorry for the details guys : / Does anyone know what the green mucus could