I woke up with terrible knee pain?

This morning I woke up and my knee was almost unbearably painful. I have only been doing my usual brisk walk during the day as I have for the last few years, nothing strenous that might cause injury. There is swelling, and its sore to touch to the right side of the patella, and the pain seems to be coming from in under the patella. My knee cracks really bad each time I move it, even if its only a slight movement. Its is getting quite hot to touch, which makes me think infection, possibly tendonitis. I can hardly walk, and can't see my doctor until friday. Please, any suggestions.