Good Evening. A Couple Of Weeks Ago I Fell On

Good evening. A couple of weeks ago i fell on my knee at work onto a concrete floor. It was quite painful at the time but as the day went on the pain subsided until i thought it was completely gone. I have since noticed that touching (even lightly) on the lower part of my knee cap causes extreme pain. I have no pain in walking..bending etc (kneeling on that knee is out of the question). What would you suggest the cause of this would be?