what did I do to my leg?

A while back I fell going up some stairs and thought I broke my legs I hit my shins so hard. For a year and a half that spot hurt so bad even if it was barely touched. Well... Today I tripped and rammed an L cart into that same exact spot on my leg, and it hurt so bad! I Ended up going home from work, and on my way I noticed my leg has a HUGE bump on it now. And it s throbbing sitting standing whatever...
When I walk I can feel pressure in that spot and shooting pain go down to my ankle. Also when cold air touches it, it hurts... Why? What did I do to it?