I'm a guy, and I'm not a doctor. I saw your post on the main board page (it was tough to miss the ALL CAPS!).
Now that I'm done with the disclaimer:
I've been a leader of marathon training programs and have spent hours running with women and have learned more than I ever wanted to know. And I've read a lot of training books. Believe it or not, some of the books actually have chapters dedicated to issues with women's bodies relating to distance running.
If I remember correctly, the primary cause of what you mention has to do with the way marathons can release many hormones into your bloodstream.
Although this is mentioned as the primary cause, and is not really a big problem, the books always say that you should check out any irregularities with your doctor to rule out more serious causes. The doctor may want to take blood tests at different times to check hormone levels, etc...
Good luck, and way to go for finishing the marathon.
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