Whats happening to my knee?

ok, so i don't really know how it happened but my knee hurts every time i jog run or sometimes walk. it's stopping me from doing what i want. i don't want my parents to know beacause they will disallow me to play netball and do athletics which i really want to do. is there anyone who might have an idea how i can support my knee? (so i could still posibly do well for sports?) sometimes i can't put weight on it and it feels like it's gonna colapsise but it doesn't, it also sometimes feels like it's being popped out of place. i did gymnastics a few years ago for 4 years, would that be why it's playing up?thanks heaps!