Iliotibial Band..?

Dear Runners,

 I have been training for the Zurich Marathon, which takes place in 4 weeks, and I have suddenly developed an injury. 

 Last weekend (Sunday) I completed my first 20 miler with no problems;  I then attempted my normal 7.5 miler on Wednesday but at around 6 miles I had to stop.  I had a severe pain in the side of my left knee.  Anyway I stopped the run and did my usual after-run stretches.  I didn't run again until Friday (two days agao) and to my horror the same thing happened at almost the exact same time. 

I have since self-diagnosed (could be wrongly) it as a problem with my Iliotibial band and have taken measures to hopefully rectify it.  Namely certain stretches on a daily basis, regular icing (not the baking variety) and my wife, very kindly, massages it nightly.  I have also given myself 4-5 days off from running.

However, I am of course scared and perturbed about what will happen after these 4-5 days off?  Will I be able to run the marathan in 4 week's time?  What else should I be doing?  Basically, please help.

 Many thanks in advance of any advice no matter how small.