Thanks for the thoughts Luc! Today it's not hurting very much at all.
If it is the beginning of a stress fracture, its not very bad yet and
hopefully it will heal quickly. Either way, I'm taking this as a sign
of overdoing it and I'm going to back off.

Ron and Ryan, thank you for the suggestions! I think I have a good
plan now for when I start back. I'm going to spend some time working
on conditioning and form before attempting to build significant
mileage again.