I cannot be sure what the discharge is. It may be a manifestation of malabsorption - in which case further tests with fecal fat tests or workup for celiac disease may be considered.
Irritable bowel syndrome is associated with increased gas and bloating - which may partially explain your symptoms.
If you had a sigmoidoscopy two years ago and you continue to have symptoms, I would consider a full colonoscopy to better evaluate for diseases such as inflammatory bowel disease.
If the cause is truly determined to be constipation-predominant IBS (and if you are female), you may want to consider a trial of Zelnorm - which is used specifically in these cases.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.