It could be a matter of lack of circulation due to lack of movement. While setting at your desk rock your feet back and forth from toe to heel. Then raise your left leg up in the air and put it down, then raise your right foot in the air and put it down. Do this 10 times for each leg. Next make a big circle with your left leg and then do the same with your right leg. Repeat all of the above 10 times ever hour. If you can and are allowed - walk in place at your desk for 3 minutes. See if this doesn't help with the swelling. If it does not, I would consider seeing a doctor. There are numerous reasons for swelling and some can be serious. I hope this is helpful and takes care of the problem.
