Sprained Ankle, Swollen. Why Is It Not Subsiding?

I tripped on a weird curb and sprained my right ankle. But when I fell, I also went down hard on my left knee , ripping a hole in my jeans and causing a skin injury. I rested a while, and then got up and walked, mostly concerned about my ankle. However, as I walked, I could feel the area just below my left knee swelling , and by the time I got home, it was as big as a softball! There was no bruising, although there is a little now, on the side of the knot . I put ice on both the ankle and the knot, and that reduced the swelling by at least 2/3. However, the knot is still painful to walk on, and the ankle is not very painful at all, though it is still swollen. Any idea what the knot could be, and will it just go away on its own? I m trying to keep both legs elevated as much as possible. YYYY@YYYY