Dear Riley, Structures that can create a pain on the right side under the ribs include the rib cage musculature, the diaphragm, the pleura (a thin covering over the lungs), and the liver (slightly lower down). Conditions that may cause these structures to have a painful experience include blunt or sharp injury, sprain of the muscles/ligaments that form the rib cage (the most likely cause at your age, and self-limiting), a patch of lung infection (pneumonia) (but in this case, you should also be having high fever, cough and phlegm), exhaustion of the diaphragm through heavy running or physical exertion, and liver inflammation (hepatitis). To further delineate the problem, you would have to see a doctor, if simple liniments or pain-relieving ointments do not help.