I had that pain once and discovered I had costocondritus (sp) and pleuresy. I was in the hospital a couple days. Go to an ER or urgent care facility.
i know this isn't probably what you want to hear but i had the same thing it was sudden and severe. Mine was displaced pain from a appendicitis. I've had an apendectamy and that pain is gone (now i just have pain from the surgery) either way... i'd get to a doctor. I went to the er.