What Causes Pain In Knee When Sitting For Long Time?

I have just finished the cross country season and I am a first time runner, well in August of this season (2010), i landed awkwardly and sharp pain came to my knee and my coach and i decided it was just a new runner's kind of injuring. So I iced it and it controlled most of the swelling. It felt better. But ever since then, every time I sit down for more than 30 minutes, it hurts. So do you think there is a problem?