When I Was Playing Soccer Somebody Fell Into My Right

When I was playing soccer somebody fell into my right knee and it bent backwards a bit. I couldnt put any weight on it for about 20-30 seconds then i gould but it still hurt. Whenever i put any weight on it while it is locked or straight there is a sharp pain inside my knee and my leg sometimes gives out. I can still walk fine though but im scared to run just in case i injure it further. Ive searched a while and havnt found anybody with the same thing. Can you help tell me what this is and what to do?