Replying to Pain behind the knee?

Hey guys, so this past month has been going great for me in terms of skiing. I have been able to go up about 7 times and I have enjoyed every single time of it. There is only one problem. About the second time up I have started feeling this strange pain right behind the joint of my knee. It almost feels like the tendons have been stretched or stressed extremely. I stretch daily and try my best not to worry about it. I have been charging hard the first day up, I have been learning new tricks and trying my best. But, I wonder if something went wrong when riding switch? Pain seems to hurt the most after landing switch and I am very nervous about landing now. I have heard things about DIN marks on skis that could affect joint and knee pains. Does anyone else out there seem to have the same problems with pain? I feel as if I might have torn something. I feel it the most when my legs are stretched out as far as they can go, or when I land a little backseat. My friend had also torn his ACL last year and before that all happened, he had pain in his leg which he iced off and seemed to be fine. Could this be leading to a torn ACL? +K for help and suggestions.