Hops is a very old remedy that is useful for cramping and anxiety/irritability during PMS. You can get hops tea at some well-stocked natural food stores, or order it online. Be careful to get a good brand and not just bulk hops in a sack, since there is a VERY bitter component to the hops flower that makes an unpleasant tea. I used to use this when I was a teenager and had terrible periods that lasted for ages.
You can also just have a beer
Something hoppy and unfiltered like Sam Adams would be a good decision. It's not as good as the tea but if you have enough beers you may not care anymore.