Sorry you are in so much pain,
I myself have had several abdominal surgeries and the best way to try and lessen the pain when you are trying to sit up or even move at times is to keep a big pillow handy and press it firmly on your surgical area before you move. This supports the muscles and lessens the movement around the area. Movement is important, this may sound strange but... The more you do move the better you will feel. Use the pillow to do your deep breathing exercises and cough so you will be less apt to get fluid build up in your lungs. If the pain is increasing or seems different please contact your MD, Not an area to guess with thats for sure.
Hope this helps