answer:My first thought: Kidney Stone. But it could be anything from constipation, bowel issues or diverticulitis…since you say you’re small and fat, it could even be left side liver pain. I am not a doctor. If this were me, I’d clean up my diet even more to see if it subsides: Skip the dairy, eat more fiber, look at the waste exiting (note the color and shape), eat more greens, then. I’d contact the doctor if it doesn’t go away or it gets worse. EDIT: Does this pain subside when you walk or exercise? Or does it worsen?