I have the exact same thing but I think mine is due to lack of muscle tone from being hospitalized for so long. I've lost a lot of weight since my surgery but my lower abdomen is sticking out so much that I still have to wear the same size pants. It's very frustrating! Anyway, back to you! Swelling is definitely common for quite some time after surgery and it should start to go down soon. If you are really concerned, you might request a CT scan from your doctor. That would show if fluid was accumulating in your abdomen. Good luck!
Diagnosed with Crohn's in 1988 (age 7)
Ileostomy Nov 2006