A very normal problem!
Most of us experience pain and stiffness, with or without swelling, with prolonged sitting or standing for a few months post op.
I coped with it by figuring out my sitting comfort time and setting a timer. It was initially five minutes, then ten, etc.
During my first two months I needed to ice and elevate after the timer went off. After that, just getting up and walking a few minutes was enough. However, with the swelling you're experiencing, ice and elevating "toes above nose" for a minimum of 45 minutes several times daily is essential.