With a recent colonoscopy being negative, it would be unlikely that any major disease (i.e. cancer) is responsible. It is also possible that the area of tightness can cause the stools to be flat. There are some cases of irritable bowel syndrome that can affect stool shape.
A few words on how stool is formed can be found here:
http://www.fruit-eze.com/education/colon/stool.html
and here:
http://www.drmirkin.com/archive/6864.html
If you continue to have symptoms, then gall stones are certainly a possibility. An abdominal ultrasound would be the most appropriate test to evaluate this.
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.
How can I fix it. I think i bured the contraction effect on my intestine and its not pushing through the stool. Not its flat and only some stool comes out at one time and it definently look different. Please some advice
T, Thank you.