Could be patello-femoral joint, or just plain contusion. With a contusion, you'd know because it's tender to the touch.
with the joint, if you can get past touching the skin, straighten your leg and relax your quads.. you should be able to move your patella around without pain. If moving your patella around is painful, like a deep boring bony pain, then you might have some damage at the patellofemoral joint (knee cap undersurface).
typical ice, rest, maybe you can rub some kind of topical pain cream for the pain.
If it's been hurting for a month, you should feel like it's getting better. if it's getting worse, go see a doctor for x-ray
