What could cause extremely painful (not just a little pain) bowel movements?

Painful BMs. Painful and extremely painful bowel movements can be caused by hemorroids, anal fissure, proctitis, anorectal abscess, acute prostatitis and anal and rectal cancer the pain can vary from slight to extreme depending on how advance the condition is some other causes are crohns disease, ulcerative colitis and endometriosis.