In addition to natural progesterone, there is another natural remedy that I swear by (as does my honey, who can tell you in no uncertain terms that it makes a world of difference).

Extract of chaste tree berry.

While it is estrogen dominance that makes for the symptoms of PMS, it is an overabundance of prolactin that causes the imbalance (prolactin inhibits the bodies own normal production of progesterone). Extract of chaste tree berry inhibits prolactin, and helps the body to find a normal balance of it's own estrogen and progesterone.

I can tell you, without it, my responses to trolls here would be much less civil.