Inside heel – running injury?

I’m a longer distance runner. After feeling slight discomfort in my left heel after hard or laong runs for a number of months I definitely sprained something at 9km of a marathon about a week ago. Although I stubbornly continued and finished the race, it has been quite sore and swollen on the left inside of the heel for a week now. I had one session with the physiotherapist who traced the pain also to my calf muscle. Is this a unique injury, common and what is best treatment please?