My wife and one of her best friend both used to get irritable with cramps before and during their menstrual flows. I got them both to start taking magnesium supplements regularly. They no longer have cramps, and, while still "irritable" at times (*giggle*), it's not a result of the menstrual cycle.
I believe Cathay's suggestion of Coral Calcium also includes magnesium in a highly bioavailable form, and so that would probably be just as effective.
You might also want to look into boron's role in estrogen regulation and osteoporosis reversal.