I'm young and healthy too, and I (very) occasionally have bouts of insomnia. It's usually stress-linked. Last year I was finishing a big project that involved lots of physical labor. Trying to work outside lifting heavy things in August SUCKS when you've only slept 2 hours the night before.
As hard as it is, just cut out caffiene entirely in this circumstance. Drink lots of water to make up for it. Caffiene stimulates the production of the stress hormnone cortisol, which can stay in your system for 18 hours after drinking coffee. So if you're already stressed you're just overtaxing your body even further.
Legion, it sounds like you were overtraining. A very common problem, but I doubt it would happen to someone running 18-30 miles per week.