What Causes Persistent Swelling And Pain In Ankle?

Hi, on Halloween of 2009 I slipped down some stairs and fell on my left ankle and I heard a loud crack, It swelled for weeks afterwards and I had went to the hospital and they took an xray of my ankle but found nothing wrong, they told me to stay off of it for a week and come back if it wasnt healed in two. well in that time I ran out of insurance and could not go back and here we are over a year later and my ankle is still giving me trouble. It gives me moments of dull pain in the original area of where i fell on it and over time it progressed to go to other parts of my ankle specifically right across from where the original injury was. Why is my ankle still giving me troubles? i can not wear high heels anymore because of it and if i sit on it or stand on it too long it causes me pain or if i put too much stress on it... Why is it still giving me trouble a year later?