What Is Causing An Abnormal Protrusion Of My Ribs With Occasional Pain?

My rib on my left side is sticking out abnormally, i used to get random pains , maybe three times a week, but two days ago i did a fifty meter sprint in gym class,( which i have done before), and now it doesnt stop hurting. It feels as if there is a bruise there, and it hurts to lift things up and move in certain ways, i got x rays done about a week or two ago and they said everything looked fine