Constipation occurs when bowel movements become less frequent and make it difficult for stool to pass. Constipation happens most often due to changes in routine or diet, or due to deficiency of fiber. When constipation is left untreated, it can lead to a medical complication called rectal prolapse, a condition in which a part of the intestine gets pushed out through the anus because of excessive straining. You should see a doctor for constipation treatment if you have severe pain or have blood in your stools or when constipation lasts longer than three weeks.