What Causes Swelling Of Stomach And Hardness After Undergoing Open Appendectomy?

Good afternoon. Five days ago I had an open appendectomy, I m at home now and the only instructions I received were to clean my wound daily just with soap and water. I don t feel very much pain therefore I m not taking any pain medicine (The doctor said only if it hurts, take it). I can eat normally and evacuate normally, I m walking and trying to sit down rather than lay down, also the wound seems okay, no swelling, no redness or warm to touch. The question I have is, my belly looks swollen, not precisely the wound but my abdomen, just when the stomach ends and the bowel starts. And when I touch it is hard (hard as if I take air into my mouth and my cheeks inflate and I touch it, like that) Is it normal? It s because of the surgery? Thanks for the answer.