pain in side of heel under ankle

I have had a pain in my right foot on the side of my heel under my ankle. It looks swollen compared to the left foot. It feels like a combination of a deep stretch and a numbing pain when I push off of my foot (as in jumping jacks), or if I balance on this foot to bend down and pick something up, or when I kick this foot out in front of me. I went to a podiatrist in November who couldn’t find anything wrong despite an exam and xrays. He told me to take naprosen and get insoles for my gym shoes, but not to limit any activity at all. However, I got the flu and so I didn’t do any working out for the next two weeks and the pain went away. Now it’s back and I’ve rested it a bit but it won’t go away. Any idea what this is due to and what can be done about it? I used to run before I got this and I’d like to be able to again.