From TomFost: (TomFost)

I had the same problem after the 1993 Marine Corps Marathon. Since I wanted to continue running, my doctor told me to increase my mileage by no more than half a mile per week beginning with one mile. If the pain returned, he said to STOP. Running further would only bring me back to square one. ITB can take months or even years to heal. Mine took six months. For a long time I could run only about 20 minutes. Suddenly, one day I ran 38 minutes. It improved from there. My doctor's sports trainer also suggested daily stretches to elongate the band, which starts at the hip and ends at the knee. This is the easiest: Stand with feet shoulder-width apart. Bend over and grab ankle of injured leg. Bend at knee and raise ankle toward waist. Lift ankle as far up as possible. You should feel it in the hip-buttocks area.

Good luck.