Sprained knee?

Yesterday I dont know what I did but I probably twisted my knee to fast to far the wrong way.Today It hurts to walk on it and it hurts to climb up and down stairs, to bend my knee, or basically move it in any way. I've sprained my other knee before and I've had alot of the same symptoms but last time I felt a pop. It also hurts to run, hop, etc. but I havnt really done that. It also hurts to push out with my knee when I scoot out my chair from out from the table or scoot it in. I am also 14 years old. and should I get a note for gym cl. What also do you think is wrong and should I be on crutches or what.