I agree with Barb. I keep my calories between 1100-1400 but occasionally I've had as many as 1600 or so, and it's amazing, when I do that for one day, I almost always show a loss the next day or two.
So now I allow myself a mix-up day here and there and add calories and it seems to keep the weight coming off. Also, to change the amount of exercise although it sounds like you are doing alot. Have you seen a nutritionist or checked with your doctor? Metabolism is a mystery to me sometimes.
You can certainly be pleased with yourself for pursuing such a healthy lifestyle and wishing you lots of success in your marathon. No matter how much you weigh, you're my role model for all the self-care you're doing!!
How many calories are you eating each day? Maybe you aren't getting enough calories; or maybe you just need to vary your calorie intake/exercise routine a bit. Sometimes, if you do the same thing all the time, your body becomes used to it and it's no longer a challenge.