What Causes Constant Pain In Leg Below The Knee?

Age 45, weight 225, height 71 . 3 days ago I woke with slight pain in my right leg right below the knee near the top of the shin bone. As the day went on, it became more painful. The next day I rested it and it the pain subsided but I noticed it was swollen from my knee to a couple inched above the ankle. Day 2 the pain lessened but the swelling remained. Day 3, I noticed the pain has extended down the shin bone to just above the ankle and when I press into my skin, it leaves an indentation for several minutes. The night before this came on I drove a bus in cold weather to a tennis tournament and was in/out of the cold all day.