This is most likely because of fissure in ano which means that near the anal opening, due to chronic constipation, sometimes a cut like lesion develops, which leads to severe pain while passing stools(poop), constipation (unable to pass stools) and sometimes blood in stools. A trial of conservative management ( medicines and lifestyle modification) can be given.

Looks like Anal Fossure (cut in the anal skin due to constipation most likely) Start sits bath (sit in like warm water 4 times a day in a big tub for 15 minutes), start on laxatives (Duphalac 3 tsf at night), eat a lot of fiber and apply ointment Anobliss after sits bath. And you need a surgical option to examine the lesion to confirm the diagnosis, it’s very important.

Take surgical opinion and proctoscopy clinical test. You will need colonoscopy with biopsy High fibre diet like fruits and vegetables and salad Stools softener like syrup cremaffine plus.