Have you had any surgery in the past 10 years or so? If you have and it involved the internal torso, you might have the doctor check on the possiblity of "scar tissue" that could have developed and could be constricting parts of your large or small intestines. It happened to me, and I went for 12 years with excruciating abdominal pain...had 3 kinks in my small intestine due to this tissue, and everything else was "stuck" together by this tissue. The sigmoidoscopy did not show this problem. What a relief when they finally cleaned it up! They were also surprised that I did not have a major problem, such as bursting of the small intestine. It's worth asking about.