Andrea, I haven't had a cycle in several years (I'm still in my 30s, not menopausal yet). Finally went to my dr. in January and she told me I was hypothyroid and prescribed synthroid. She said that may have contributed to no cycle.
I'm still not having a regular cycle, even with Provera, but my dr. did say that the hypothyroid could be contributing to no cycle.
That's kind of the opposite issue from what you're having though.....so I don't know if that helps you or not, except that I understood from what she said that your thyroid levels could affect your menstrual cycle.