So sorry about your ITB. It sounds like it might be brought on by fatigue and getting out of alignment. Do you tend to overpronate or step across the ‘center line’ with either foot? Usually, either of those can contribute to ITB syndrome. As you are running (and walking!) it’s important to make sure your feet are tracking straight, as if they were straddling either side of a line. If one foot splays out, be sure to rotate your whole leg inward to align it again, not just your foot. And if you tend to step in toward or across that line, you might be losing your core engagement, might need to work on strengthening your glute medius, at your hip.
If your habit has been to do one of these two things, and you have been working on alignment, they still may creep in when you get tired. Or if you have been moving out of alignment for a while, the symptoms will eventually show up. Be sure you are practicing good alignment and posture ALL day long - not just when you are running. Chi Running is about becoming aware of your body and making that mind-body connection so that when you are standing in line or washing the dishes, in the ‘background’ there is an awareness of how you are standing. Keep practicing that.
If you can do a run-walk (see http://www.chirunning.com/learn-it/chi-walk-run), it will help you get through your long distance and the walk part will help you hit the reset button, and realign. Don’t wait til your body yells at you - practice it at the get-go.
Keep us posted and let us know how you are doing!
Certified Chi Running and Chi Walking Instructor