Behind The Knee Pain More Condition_symptoms Why Have I Got Pain Behind My Knee?

Why have I got pain behind my knee? - behind the knee pain more condition_symptoms

I left my car this morning when I went it was a pain in the back of his right knee. I thought it was a chain to pull the thigh and calf in this together, and is painful when I walk but it feels good when I feel the feeling, but something that is very firmly behind the knee. I can still walk, but it is more of a limp. I tried stretching, but to no help.
What have I done?
How can I do better?