Originally Posted by late
The only other thought I have is that your ITB may be really pissed off, and that even small amounts of use will set it off.
That indeed can be the case. Just when you thought it was safe, you only need to mash a gear at the wrong time, and it comes surging back again. Rest is good. Spinning is good. Staying away from steep hills is good. Float in pedals (I use Time Atacs) also is good. And in my case, I use platform Time Atac pedals (as in MTB) to keep the foot from pronating too much.