Congratulations on the donation and how wonderful for the recipient.
You are very early in your healing. You don't really start to heal until the 3rd week. It might be a good idea to slow it down a bit. Just easy walking, slight stretching, and not more than 10 lbs at any time and only for a few reps. You had a lot going on inside of you during that surgery. A lot of organs were moved and jostled, connective tissue was cut to get to the kidney, then that was cut out, and then everything was sutured back together.
I didn't start to drive until the 3rd week, my doctors orders. I think that with all the activity you are irritating the surgery site, causing a fluid build up in you abdomen. You might benifit from lymphatic massage which your co-ordinator should be able to recommend to you. But please slow down, you only get one chance to heal.
When sitting put up your legs up so your feet are even with your heart. That will help the fluid get moving from the bottom half of your body.