As ordered by my doctor, I saw a physiotherapist today. Background on what got me to this point can be found here.
The therapist heard my story, asked some questions and performed some tests. He feels my calf muscle and hamstring is far too tight. He suspects the run that shut me down was just the tipping point. The fix is a great deal of stretching, focusing on my calves, hammy and IT Band.
The stretching, combined with regular physio treatments, isn't a quick fix. There isn't a quick fix. I've got to put in the time if I want to run longer than 2k.
I'll stretch like crazy for a week and then test it again.