I Have Severe Rectal Pain That Worsens Shortly After Bowel

I have severe rectal pain that worsens shortly after bowel movements. I just had a colonoscopy and it was clean . I've had a cat scan using barium it was fine I have had four finger rectal exams by different doctors showing much tenderness in the prostate region but no swelling of the prostate. What could be the cause of the severe rectal pain?