Maybe you're trying to go out too fast. I had the same problem last year when I had a three month break over Christmas. To make myself stay at a good running level, and not run out too fast, I started using a heart rate monitor and stay in HR zone 2, which I think is between 70-80% of maximum HR (can't remember off the top of my head).
I'm pretty sure you could get back to where you were, 5 months is a long time, aren't most marathon training plans under 5 months anyway?
Good luck with the training and getting that sub 4 marathon in Chicago
Hope everyone's training is going well. Good luck for the tri tomorrow Tim!
Just joined the local tri club so I can do some open water training sessions. I found out last week that my current goggles are useless for open water (they're not tinted and can barely see out of them), has anyone got any suggestions for open water swimming goggles?