About 2 Months I Noticed A Knot On The Back

About 2 months I noticed a knot on the back of my right foot above my heel and right below my Achilles. It is sore and it is hard almost like a bone. It is painful. Kind of a dull achy pain. It hurts when I first stand and walk and then the pain gets easier. It is sore when I press down on it with my fingers. This foot was badly sprain 8 years ago. What could it be? Should I see a foot doctor or my general doctor?