Swelling is just under my right ankle (outside). Most of the pictures I have seen show that this looks to be area peroneal tendon area. I have redness and swelling. My doctor gave a corticosteroid injection on the inflamed area. I had no injury. The only think I can think is that I was painting my basement for long hours barefoot on hard wood floor. Also I have flat foot. I have anti inflammation medication for almost a month. Will start physio. in couple of days. Not sure what can I do. My Dr. is not really able to figure out the exact cause.