What Causes Severe Pain In Knee After Lifting Heavy Weights?

I'm an athletic 20 year old female who lifts heavy weights in the gym frequently. During my last gym session, I squatting a lot more weight than usual as well as leg pressed a lot more weight then usual. Right away I noticed severe pain in my left knee located on the outside part of my knee. It hurts to bend and straighten my knee, it's stiff, little swelling, it clicks and pops when not wrapped, it hurts to walk on so I am limping around, I can't keep it straight for long periods of time without feeling pain and it tends to give out here and there. I have had knee pain in the past from running. Could this be a tear or a sprain? Where abouts in my knee would the tear or sprain be located?