HI! im a 15 male who has a history of ligament stretched ACL and PCL after 6 months my doctor said that i can now play my sport pingpong. Today when i woke up my back of the knee started to be painful i don,t know why when i stretch it its like its gonna pop! it hurts like when you are trying to pop your fingers, then i cant walk properly. I think it is caused by the cool temperature when i woke up and my brothers leg (so heavy) always put it to my left leg (injured)