If the pain is on the outside of the knee, then it sounds exactly what my husband had. The pain always came on at about 2 miles, and his is due to his ITB. He has been working extensively on rolling it on a foam roller and stretching it daily, this has helped tremendously, and he can now run a lot further. Might be worth booking a session with a physio with the marathon being so close. It will be painful, but may be the only chance you have of getting back on some sort of schedule quickly. Resting does not address the problem of a tight IT band, when you start running again the problem will still be there.
Yes, we did. We were trying to get with the R/W pacers we wanted to run with. When you go in the ballot having not run a marathon, it is difficult to predict a finishing time. I'm sure many peoples times change drastically from what they predict.