Knee pain and need help? ?

I was palying soccer and i was running for the ball. I reached the ball and i pulled it to me, then after i placed my foot on ther ground putting weight on it, my knee cracked i felt as if it mooved with instant pain in the back right side of the knee. I was able to walk and it did not swell instantly. The day after my knee was really swollen and it hurt in the back right side of the knee when i bent it and it also seemed unstable when i stepped. I went to the doctor to get it checked and they told me it wasnt a ligament but i dont know what it is.