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I think the medroxyprogesterone is a good idea. For some reason, you are building up your uterine lining, and the progesterone should help to prevent that buildup.
As long as your D&C's have had benign findings, I don't think that you need a hysterectomy. The bleeding and the buildup of the lining are somewhat strange, but they can't go on forever, and there is no indication of cancer.