What Causes Soreness Of Leg?

Hey - I have a somewhat random question but I would like to ask anyway in hopes of getting an answer. For the past maybe week or two my right leg has been.."sore" Initially it was a little sore below my knee in the back, and now it is sore in the back a little above the knee in the back of my muscle. I watched Doctor Oz before and he said this could be signs of a blood clot. I sit at a desk most of the day, and I don't get much exercise but I'm not actually overweight. I've never had my cholesterol tested but I eat a lot of butter and cheese. I was just wondering does this seem like something I should get checked out? or am I just being paranoid? Did I mention I am only 20 years young??