Have you been sitting more than usual? There is something called dependent edema that is basically gravity at work if we sit too long. The legs and feet tend to fill up with our excess water.
Move around more and watch your sodium intake-- 2300mg is the daily req., but you may be sensitive and have to watch it more. Also lay down and put your feet up for 20 or 30 minutes. I have this problem and since I did not take care of it when I should have I now have permanent damage in feet, legs and ankles meaning the swelling never goes down.
If it does not clear up, I would see a doctor as there are some other things they might look for.