I have a pain on my left side that comes and go i feel as if its somewhere under the ribs. what could that be and what kind of scan would i need.

Left side: Pain in that region could come from abdominal muscle,spleen,base of the left lung or rib cage,lateral aspect of the stomach or pancreas or the splenic flexure of the colon due to gas entrapment or inflammation. At your age and if there are no lung, bowel symptoms or rib cage tenderness, I would start with an ultrasound of the upper abdomen and,of course, a physical examination by your physician.