Mamallama,
You're doing awesome. I have just experienced not running consistently for three weeks and am now paying the price, especially w/ the event coming up on Saturday. RAR told me this morning that she had heard a statistic that said that for as long as it takes you to train for something it takes half that time to lose everything you've worked for if you stop. I think you get the jist of what I'm saying. I don't think you're talking about quitting, but it's just something to think about. I also remember someone posting on here (I'm too lazy to find it) that when you're feeling sluggish and feel like you've reached a point where you can't get your body to go any further it's time to pull out the weights. I remember them saying that that is called plateauing and that requires a booster shot (weights) to get you out of that. I found that it was helpful to me, at least up until I stopped training aggressively.
It blows me away that the human body can carry itself 26 miles. You're so awesome to attempt this. I don't want to pressure you into doing the marathon, especially if you are wondering if it's unhealthy for you so don't take my encouragement as pressure, please. I just want you to know that I believe in you. I know, based off the experiences you've shared with us on this website, that when you put your mind to something that you can accomplish it. You are a woman of great strength. It has been fun to read about the spiritual enlightenments you've received on this journey and I'm sure as soon as you get through whatever you're going through, you'll have another one to share w/ us. It's amazing how Heavenly Father speaks to us and teaches us what we need to know right now. I know that when you do decide what you really want that Heavenly Father will be able to help you achieve that. As silly as it sounds, the Savior's Atonement applies even to this.
Like I said, please don't take my encouragement as pressure. Remember that you made a
choice to run the marathon and the beautiful thing about choices is that you can always choose again. You have not signed an unbinding contract w/ this marathon so take the pressure off yourself that you
have to accomplish it in May. A 1/2 marathon is a huge accomplishment and, quite frankly, so is a 5K.

Anyway, I think the most important thing you can do for yourself is listen to what your body is telling you because when you do, you'll know exactly what your next move is. I'm not sure that this made sense so I'm gonna go now because I feel like I'm rambling. Good luck w/ whatever you do!!!!