I am not a heel striker. I am more of a mid/forefoot striker. For the past week, the back of my heel (not the bottom, but directly in the back) has been aching. It hurts mostly in the morning and then also for the first 2 miles of my runs, after which time it loosens up (most of the time) and then is hardly noticeable (or not at all noticeable) for the rest of the run. About an hour afterwards, I can feel the pain when walking. It isn't excruciating, but it is annoying and slightly painful. Any ideas?