Constipation
While diarrhea is a sign of something wrong with your colon, so is constipation. If you have pain or difficulty while passing stools, it could mean that there is some sort of obstruction in your large intestine or rectum which is causing this.
The MOST IMPORTANT CLUE is not one single case of constipation or runny stools, but a persistent change in their color, texture and consistency.
Additionally, you may feel the urgent need to go to the toilet and not be able to pass stools. Or you may keep experiencing incomplete bowel movements.