What Causes Pain And Swelling In The Sole Of The Foot?

Season Greetings...

I am having a problem with my foot. My sole in the left leg has swell. It is very painful. I went to the doctors but they are not able to identify this problem. The doctor gave me a medicine but once the medication got over the pain started again. Now i am not able to walk properly. Even if I do it is with pain. It is very painful.. Please help me... :)