I've Had Chronic Pain On My Left Knee. Right In

I've had chronic pain on my left knee. Right in the middle of my shin bone & knee. I've had people give me theories of what injury they think it is between ACL, Meniscus, or Patelar Tendinitis. At one point it was swollen but it feels fine until I go and play basketball. I play on the team and after a time of playing hard it eventually starts to hurt a lot and especially when bending my knee to shoot. I was wondering what it could be? I thought patellar tendinitis was the most accurate description of what's happening. If it is tendinitis - how would I treat it ? Please help it's been like this since last February