It is not uncommon for there to be some dependent swelling in the legs after big abdominal surgery. Takes time for the congestion in the surgical area to resolve. Also, if you are anemic, you have less ability to hold fluid in the bloodstream. The key is to keep moving when you are up (working the leg muscles moves blood through the veins). When sitting, elevate your legs to prevent more edema (swelling).
On the abdominal pain, if it is sudden or severe, go to the ER. But, if it is just an increased soreness, it probably is likely to your increased activity.
Jan