What Causes Pain In Abdomen After Appendectomy?

Hi I have had an appendoctomoy but the surgeons said my appendix was fine but was too high and squeezed between a mass and my colon so they took the mass and appendix out. Should I be worried about the mass? Why would this be there in the first place? I am in the first week or recovery and I have pains in the right side of my abdomen, under the rib cage and lower back at times. Many Thanks Si