Sore leg since Thanksgiving. Why?

Ok so clear back on Thanksgiving, a muscle in the back part of my lower leg started hurting. It felt like maybe I had stretched the muscle too far. It has hurt since then and the pain does not go away. It hurts clear up the back of my calf, to the back of my knee. Sometimes even a little higher. Its difficult to walk. I have iced it, put heating pad on it, stretched, used pain relievers, soaked in baths... EVERYTHING. I can't figure out why this hurts so bad. I didn't really do anything to cause the pain to begin with either. I just noticed when I stood up that it hurt. I thought I stood wrong on it, my friend keeps telling me its a blood clot. What could it be and how do I get it to feel better? I hate to go to the doctor just for a pulled muscle.