My lower back hurts like its cramping up when i have to poop . if not having to poop then my lower back really doesnt bother me what could be the caus?

BombBayNeedsAnOiling: Sounds like your equivalent of a cramp. Some people get pretty powerful sensations when they have to unload. Usually it's a sense of pressure. If there is any constipation, it could get pretty powerful. But your lower back could be reflecting this. At your age I wouldn't worry about much more. If more dietary fiber and a stool softener doesn't help, see your doctor for an exam and advice.