another vote for the starts of tendonitis. Your description could be nearly identical to what I had happen to me a few years ago on the c25k program. But mine was long lasting and I ended up having to get an injection to finally calm it down after a couple months.

Rest for a bit. And maybe repeat an easier week only after the pain is gone. If it comes back or you can feel the tendon (know what I mean??) stop. And it wouldn't hurt to see a doctor... though I wish I had seen someone who was less needle happy. I can't complain much. What he did worked and I haven't had a relapse. *knock on wood!* I did stop running for about two year though. But mine hurt a lot and for a very long time before the injection.