Hi, I've had this problem for about 3 years now.
During times when I sit down for very long periods of time (5-6 hours), usually when cramming for an exam, I develop what I believe are petechiae purpura in my lower legs. They only appear up to about halfway up my calf. It comes gradually, and if I rest (sleep) and become active it gets better pretty fast. However I've had cases where I'm studying all day for several days (3-4 days of studying ~10 hours sitting down), and it gets really bad.

Also accompanying this is swelling of my feet to the point where it can become very painful to walk depending on how long ive been sitting.

These symptoms only seem to ever appear when sitting for long periods of time like this. Thanks for all your help.