I'm having pain during defecation and last night there's blood coming out when i defecate . a lot of blood. what could be the problem?

Common things: To think about that could cause this are hemorrhoids(which are dilated blood vessels in the area of the rectum/anus) or anal fissures(cracks in the skin around the anus). There are other things that could be causing this too, so I would strongly urge you to see your doctor to get a better sense of what is going on with your body. Best of luck.