How Can Knee Pain Caused By Trauma Be Treated?

Hi, Im a 30 year old male with no real past medical history problems. I'm in great shape and I am training for a military competition. Yesterday I was swimming with fins in a river and I hit my left knee on a log submerged in the water. I continued to fin but with pain. When I got out of the water I could hardly stand up, but then I was fine. I had trouble getting in and out of my vehicle. My knee only hurts when I flex my knee. I can move my patella, there is no pain around my patella only on the top portion, I can pin-point it and it where the rectus femorus tendon meets the patella. It almost feels like a nerve, because the pain shoots up and I reflex to counter the pain. What can it be? and how long will it take for it to heal? Thank you