L.S.
How old are you? You may be experiencing premenopause. I got a book called "What Your Doctor May Not Tell You About Premenopause." It describes the many symptoms of estrogen dominance, which most women have. My nutritionist prescribed a natural progesterone cream, which helps with many symptoms.
Also, check out this website:
http://www.womentowomen.com/
Similar concepts.
I think your period is happening every two weeks because you are not ovulating. The progesterone cream helps with that. I've had that happen a couple of times.
Best.