What Causes Chronic Diarrhea With Stomach Ulcers And Inflammation?

My colonoscopy showed nothing abnormal in my small and large intestine. However, I have had chronic diarrhea for many years that recently started to smell like the worst colostomy bag I have ever smelled; as I am a nurse aid. I am now have large amounts of mucus mixed in as well. I get diarrhea no matter what I eat or drink. I am sick of feeling sick. I also had an endoscopy where my doctor found bleeding ulcers and bad inflammation in my stomach. Do you know what could cause these symptoms, but does not show up in view on a Colonoscopy exam? I m otherwise healthy. Under 40. With no family history of illness.