What Causes Foul Rectum Odor With Frequent Bowel Movement?

Hi there,
My name is Ryan. About 8 yrs ago, in January of 2002, I was diagnosed by my old family doctor with Irritable Bowel Syndrome. In January 2006, 4 yrs later, I had attempted to relieve myself of this IBS, so unfortunately, I stuck something quite large up my anal orifice. I noticed immediately, I had to have a bowel movement and when I did, I also noticed immediately, a foul rectum odor, that wouldn't go away with simple showering or bathing! This fecal body odor problem, has now been going on for 6 yrs and it's been very hard, as this problem, has affected my self esteem and confidence as an individual!! I have already had 2 colonoscopies and the results came back: negative on anal fissures, fistula's, internal hemorrhoids, bacterial infections and anal incontience. I am really confused about this, as I have no problems with constipation, as I can have a bowel movement, up to 3 times a day! So, I don't believe constipation to be the issue here! I could really use some help here! I know I have a physical external issue, but I don't know what I have?????? Please help me!!!!!!