Disorders that can cause rectal discomfort include:
Ulcerative colitis: This autoimmune disease causes inflammation in the rectum. This can create a feeling of incomplete emptying after a bowel movement or an urgency to have a bowel movement right away. It may also cause rectal tenderness or pain with a bowel movement.
Clostridium difficile colitis (antibiotic-associated colitis): This infection in the colon causes diarrhea as its main symptom, but it may also cause crampy pain in the rectum.
Constipation or fecal impaction: When constipation is severe, hard, dry stool may build up into a blockage called fecal impaction. A fecal impaction can cause nausea or abdominal pain. It also may cause feelings of the rectum being full even after a bowel movement, or it may cause pain during a bowel movement. Due to contractions of the colon above the level of a fecal impaction, some of the stool above the impaction is liquid. Liquid stool may intermittently leak around the impaction, so diarrhea can be a symptom of fecal impaction.
Hemorrhoids: Hemorrhoids are enlarged veins just under the anal surface. They can cause burning, itching and irritation at the anus or an aching feeling in your rectum. You may be able to feel hemorrhoids as a swelling or lump protruding out of the anus during or after a bowel movement. Bright red blood on the toilet paper or red blood that streaks the stool may come from hemorrhoids.