Upper Abdomen pain? Any thoughts on whats causing this?

Last Sunday night i noticed some mild stomach discomfort but during the week i had pain in the center of my upper abdomen. The pain isnt severe and its hard to describe but its always there. The pain is in the center of my upper abdomen just below the rib cage. I dont notice any other symptoms. My appetite seems fine and no abnormal stools. Any thoughts on what it might be and how serious it is. Im probably going into a walk in tomorrow and ill promptly make and apt. to see my regular doctor for next week. Also i should mention that i do suffer from stress and anxiety