Didn't you mix up your stride recently? I've been having extraordinary heel tightness and some arch discomfort, having worked hard over the past year to accomplish a fore-foot strike. I'm either going back to the old stride (slight heel-strike) or doing something different (like taking it easy for a long while), because this isn't how it's supposed to feel!
I had shifted to a forefoot strike. I liked it until my heel got sore. Now I have returned to non-minimal shoes, and am trying to maintain a mid-foot to slight heel strike, at least until my heel stops bugging me.