Hello - thanks for asking your question.
You note abdominal pain, bloating, gas, constipation. Sigmoidoscopy and a test for wheat intolerance were non-revealing.
You may want to consider a full colonoscopy and abdominal CT scan as was suggested by surgeon below. Diseases such as inflammatory bowel or masses/tumors would be better evaluated by the full colonoscopy.
If those tests are negative, then you may want to consider more specialized testing for your constipation. Colonic transit studies are most useful in the evaluation of patients whose major complaint is infrequent defecation. Radiopaque markers are swallowed, and their passage through the colon is monitored by abdominal radiographs. Markers are counted in the right, left, and rectosigmoid colons (defined by certain anatomical landmarks), and are followed as they move distally until expelled. Disease such as colonic inertia could be seen with these studies.
Defecography or anorectal manometry can also be considered to test the pelvic floor which may contribute to your constipation.
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.