I've recently developed a stabbing pain in my heel and I don't know what it is.

My first suspicion was plantar fasciitis but I've had that before and this feels very different. My PF was on the sole of my foot, just in front of the heel. This new pain is at the back of my heel, not on the sole at all. Also, I remember that the dead-giveaway symptom of PF is pain first thing in the morning - I don't have that. This pain is at it worst after running (it's fine *during* the run) and at the end of the day.

There's one point at the back of my heel - if I poke it there, it hurts like hell. Feels like bruising.

Not sure what has caused this. It's come on really suddenly over the space of a couple of weeks or so. I've barely changed my running mileage (I'm not a big runner - 6-10 miles a week) and I haven't changed my running shoes. No other changes in my training or lifestyle.

Any ideas?

Thanks!