Did you injure it last week, prior to the pain starting?
Is there any pain that radiates elsewhere into the thigh, or the shin?
Does the knee and knee cap itself look normal? When it feels uncomfortable -- does your knee feel unstable (like the knee joint could slip)?
No, I didn't injure it. If I did, I don't remember doing it and there are absolutely no physical signs of injury. No brusing, cuts, redness, or anything.
The pain does radiate some into the top of the shin. Yes, the knee cap does look normal although I do feel some soreness from behind the knee cap. When I stand, it does feel stable.
When people have pain that is in front of the knee, as it seems is in your case -- the classic cause of this are issues with the tendons of the quadriceps or the patella (knee cap).
So a few potential causes:
other arthritic conditions / bursitis (probably less likely than the two above)