It could be due to anal fissure. An anal fissure is a small tear in the thin, moist tissue (mucosa) that lines the anus. An anal fissure may occur when you pass hard or large stools during a bowel movement. Anal fissures typically cause pain and bleeding with bowel movements. You also may experience spasms in the ring of muscle at the end of your anus (anal sphincter). Anal fissures are very common in young infants but can affect people of any age. An anal fissure usually heals on its own within four to six weeks. If it doesn't, medical treatment or surgery usually can relieve discomfort. Add fiber to your diet. Eating about 25 to 30 grams of fiber a day can help keep stools soft and improve fissure healing. Fiber-rich foods include fruits, vegetables, nuts and whole grains. You also can take a fiber supplement. Adding fiber may cause gas and bloating, so increase your intake gradually. Drink adequate fluids. Fluids help prevent constipation. Exercise regularly. Engage in 30 minutes or more of moderate physical activity, such as walking, most days of the week. Exercise promotes regular bowel movements and increases blood flow to all parts of your body, which may promote healing of an anal fissure. Avoid straining during bowel movements.Straining creates pressure, which can open a healing tear or cause a new tear.