What Causes Abdominal Discomfort, Dark Stools And Metallic Taste In Mouth?

I have had changes in bowel movements, middle abdominal discomfort, very dark stools and a strange metallic taste in my mouth. I recently had a colonoscopy and that came out clear. With another fecal card test to be done in a few weeksl All of this is starting to cause me to wonder if there is an answer to all of these symptoms I am female and 79 years of age, mostly very healthy, with daily exercise.