Why Does It Pain To Put Weight On My Knee?

Hi, I fell directly on my kneecap about a week ago and it has been very hard for me to walk since then. Although, my knee has slowly gotten better over time, I still get a sharp pain and stiffness when I am walking downhill, uphill, and on the stairs. There is minimal swelling, no discoloration, and there is little pain when I put all my weight on it. Is it just a severe bruise or worse?