I’m a 13 (almost 14) years old, and been having knee pain in the front of my knee right below it, sometimes on the sides, and in the back for the past 3 months, with no swelling, a few to no bruises. It all started after a softball game, I was sitting on the floor and I got up, and when I went to put pressure on my leg I had a shooting pain in my knee and I could barely walk. Ever since that night every once in a while I get really bad knee pain and it usually last 3-8 days.
You may want to be seen by a pediatric orthopaedist (someone who specializes in young people's bones and joints). You can find one in your area here