Hello, have to got any injury to that area? Is the pain is in front are lateral or back side? Is there any associated cough, cold, or fever? If it's a injury then it is a musculoskeletal skeletal pain, in that case proper rest, strapping in that area with painkillers will reduce the pain. If there is associated cold then it is pleurisy in that case good hydration and paracetamol will reduce the pain. If you can't recollect anything then consult orthopedician, don't worry most of the times these pains are treated easily.