I have no medical training, so don't take this as a diagnosis. The dermatological problem makes it look more like a leg ulcer rather than thrombosis, but investigate all of your symptoms (sensation, tenderness, thick toenails, etc.). If there are other problems (diabetes, etc.), definitely see a doctor no matter what.
Thrombosis can be very dangerous because it can release a blood clot into the heart, but the skin damage seems like it could be a leg ulcer (don't let it get worse). You can find pictures of leg ulcers simply by putting "leg ulcer pictures" into your browser.
Go to this page of youtube and see many videos of thrombosis, but also look up leg ulcers (it might also be other things, so it is best to have a GOOD diagnosis from a GOOD ETHICAL doctor (good luck on that). http://www.youtube.com/watch?v=gGrDAGN5pC0
It seems to happen if you sit alot, but also blood flow can be restricted from overexertion of the leg, so evaluate all your symptoms and activity. If it's not serious, accupressure may be helpful.