It sounds like you have an anal fissure, which is a small tear in the lining of the anal canal. Most people characterize it as a continuous knifelike tearing sensation especially on defection; some people will see bright red blood on the stool or when wiping. This forms as a result of high pressure within the anal canal (usually from constipation/straining) which leads to ischemia of the anal tissue and splitting of the anal mucosa during defection. I would recommend: -All measures to prevent constipation; avoid straining and prolonged sitting on toilet. -Wash area gently with warm water -Stool softeners such as docusate daily -consume high-fiber diet and add daily fiber supplement such as psyllium -increase fluids -maintain healthy weight. -you doctor can prescribe lidocaine gel for topical analgesics -Sitz baths -Most acute fissures heal within 6 weeks with conservative therapy. -You need to be screened for infectious diseases or Crohn disease