I've had a few physio sessions.
Turns out I have ridiculously tight hamstrings. Very common in men... but a big source of injuries. In fact all the muscles in the leg run through the knee, so any tightness at all can throw things out of whack.
I have a stretching routine now that I need to do twice a day. And a few strengthening exercises. And they massaged the IT and quads.
They also did this neat thing called TENS, which is a little device that sends electric current through your leg. It feels like tingling, kind of like licking a 9-volt battery (don't try that) but in your leg. Neat sensation. Not sure if it helped with the pain, I was pretty sore, but it felt cool. :)
I should be able to try running again soon, but frankly I'm not in any kind of rush... just got the bike tuned up, bought some kick-ass triathlon bars for my road bike, so running can be on the back burner for awhile!