It hurts around the entire left knee area. I sit down with no pain but whenever I get up, the pain appears. Also, whenever I am walking up and down stairs, the pain is not apparent when walking up the stairs; it hurts to walk down them though. I am a 14 year old girl and have been playing sports for a while. Do you have any ideas on what could be wrong with my knee? If you need any additional information, just ask. Thanks!