What Causes Greenish Black Stools And Pain Between Shoulder Blades?

I have been having frequent nagging pain between shoulder blades and what feels like under my right shoulder blade. This pain is accompanied by nausea. It happens if I linger between eating but also after eating. This has been happening for about 4-5 days. Today I have had two bowel movements which I would describe as dark greenish black. I had an acute pancreatitis attack 26 years ago but don't remember the bowels issues then and the pain was more around my chest and back like a band of pain. I am a 46 year old female and I am worried about some form of intestinal cancer.