To say that you are enthusiastic about running would be an understatement. You're one of those people who seem to really only come alive when they pound the pavement. As a true amateur runner, you can only consider yourself as having really matured in your sport when you can actually begin running a marathon. If you have that kind of motivation, how do you go from running no more than 3 miles or so a day to running a shade above 26 miles? As with everything else, the ability to do something comes to you when you learn the steps you need to take and when you take them.
Novice runners believe that they need to run a good distance nonstop every day to have their efforts be of any use at all to a marathon training goal. That's not really true. You could run as far as you are able - even if that isn't a lot longer than 10 minutes at a time - and then walk for a few minutes and then pick up where you left off. It absolutely will add up. It'll add up so well that before long, you'll be able to run longer distances nonstop.
Along with the running and walking combination training method, you can actually try another method - the interval training method - to take your training forward. What is the interval training method? It's where you allow yourself to catch your breath a little bit not by walking between two periods of running, but by running slowly. You run to get a rest from running. Does that even make any sense? It does, if you consider the fact that what you need to do is to run slower than you normally do. You could try it this way - you could run the distance between the first two lampposts on your route at your normal speed, and then slow down to a jog until the next lamppost shows up, and so on. They call this interval training, and it helps you maintain a degree of interest in the whole exercise. And if you want to discuss other ways to maintain your interest, consider charging up that iPod for new and different music each day. Of course, that could end up costing a whole lot more than you ever planned to spend on running a marathon.
It's just the way the human body is built. Whatever skills you are trying to acquire, on some days, you find that you just go great guns with no effort; on other days, it seems like you can't do anything right. Here you are training to be running a marathon, and even if you've been training for three months, your legs just don't seem light and strong as they should. Breathing hard makes your lungs feel awfully strained. What you do then is that you just slow it down until it feels easy again. You don't actually have to slow yourself down to a walk; all you need do is to run as slowly as possible - even down to a shuffle. If you keep it up long enough, you'll get your second wind.
A great way to motivate yourself would be to pack more gadgetry than James Bond. At the very least, you need to make sure that you at least have a GPS watch like the ones by Garmin. It can really help you stay motivated to see your running records show up on your watch. It'll show you how far you've run and how long you've taken to do it. About the best way you can motivate yourself to practice as hard as possible of course would be to actually to sign up for a race. It doesn't have to be a marathon at all. All it needs is to be a decently long race.