Knee hurts! WHATS GOING ON?

A week ago i fell in my soccer game on turf, and got a big turf burn which stung pretty bad. I couldn't kneel on my knee for a while, but i thought that was because of my burn. Now that it's mostly healed, I tried to kneel today, and something inside my knee moved, and i was in a lot of pain. It was somewhere below my knee cap.. I can't tell if it looks swollen, maybe a little. It only hurts a little when i bend it, but hurts A LOT, when it has pressure on it. ALso, when i run, it feels like something is loose in my knee, and not right. Any idea what is going on with my knee?