Ten points if someone can tell me what's wrong with my knee ?!? ?

okay so I'm 14 yrs old female. i was playing baseball, running to first base, the first baseman stepped on my foot. It rolled my ankle and twisted my knee. this was last saturday. it got very swollen so I iced it and it felt better, but all week it has been sore on the back of my left knee and on my left ( if your looking at it, right) side of my kneecap. last night I was jumping on my tramp and hyper extended it. now it's hurting on the opposite side of my knee as well as right under my kneecap, almost on my shin. it really hurts to walk and hurts even more to bend it back or forward. it is only a little swollen. my parents won't take me to the doctor, my mom says it will go away. but, I think it is serious. the pain feels kind of twisting and it feels like my kneecap slides around when I walk. what should I do? does anyone know what's wrong? ten points for best answer!! thankyou!!