What Causes Pain And Bulge Below The Left Rib Cage?

Hi I have been having this pain under my left rib cage not my ribs right underneith. It is bulging and more painful when i am sitting. I went to the ER last Saturday and my white cell count was fine no infection they also checked labwork for my spleen pancreas and something else that all showed negative for problems. They did not know what it was the nurse spoke with me about possible hernia but dr didnt mention this and I forgot to ask him. What are your thoughts ?