severe knee pain

My knee is severely swollen as well as the lower leg.
The knee itself is very painful.
I am unable to straighten my leg completely nor can I bend it completely.
I am also unable to put full weight on that leg.
I did not injure my knee but have been walking for excessive.
I have an appointment with my Dr soon but until then, does anyone have an idea what the problem is and/or what I can do to help relieve some of this pain. Any suggestions would be appreciated.