What Causes Pain Underneath Rib Cage?

I have a pain that I get underneath my right ribcage. It feels like something gets stuck under the rib if I move or stretch a certain way, almost as if a muscle or organ is moving up underneath the rib. It happened last night but was worse than I have ever experienced before. I thought I broke a rib. I am very sore today to the lightest touch and with certain movements.