Is This A Muscle Cramp Or Injury?

Hi yesterday when i was sitting down i bent to reach something off the floor, I had what felt like a muscle contacting on my right side under my right breast near the edge of my rib cage there was a slight bulge which took my breath away slightly it was sort of like cramp. It calmed down after a couple of minutes it is ok today but feels like I ve pulled a muscle or something. What could this be?