Horrible Knee Pain! :(?

So, earlier I was outside playin an I acted like I tackled a girl I didn't like... (Yes, anyways..) an when I got up my knee hurt soooo effin bad! I fell with my nee bent straight on it... Maybe my PCL? Because I've messed that up before playin basketball an landin on it bent. I'm 16 year old girl.. I play softball.. I've had knee problems before an I tore my meniscus... I can't squat an put pressure on my right knee, when I do it hurts, but it hurts worse (to where I cry) when I straighn it out after I bend it while puttin pressure on it.. It hurts on the backside an down the top of the back of my calf to.. What could be wrong.. This hurts so bad! :'(