I Fell Off A Ladder, Yesterday, From Only About 3

I fell off a ladder, yesterday, from only about 3 feet up, but landed on my flat on my stomach. I am obese. Since then I have had blood coming from my rectum. Whether I am having a bowel movement or not. Additionally, my entire abdomen has been feeling very crampy and sore, and my lower back is really sore. I get the pain in the back and stomach, but the blood? What's going on?