Hey Dekar, i think its cos they pump you full of Co2 during surgery to lift your skin off your organs in your abdomen in order to see what they are doing, and that gas can pass into your gut anywhere along the GI tract, so your probably still full of it, and because of your surgery its harder to pass it as your bowel is healing and not working up to full capacity yet to shift the gas downwards....so i reckon if it cant go down then it has to find another place to escape, and will travel upwards....should hopefully pass in another few days, and definitely when your bowels start to work again and pass stuff through....
thats my guess tho, and if the pain was getting worse and not subsiding then i would get it checked out....
hope it disappears soon!
xx