Red raspberry leaf tea (or RRL for short). It's an herbal tea - excellent for all things womanly. You can drink it in pill form (capsule with the herbs crushed in it) or you can drink it in tea form. Tea works best, but capsules work really good too.
Anyway, I get pretty bad PMS about 3-4 days prior to my period. I start drinking RRL tea at least three times a day, and it COMPLETELY goes away. It's bizarre. It's like magic.
It sounds like yours starts much earlier. You might need to take it or drink it every day for the whole month to get it to help you, but I swear to you this stuff is amazing. Not only does it help my PMS disappear, but it also takes away cramps. For the cramps, it works just as good as ibuprofen does for me. It's so weird how well it works. Then it lightens my period and shortens it. It's awesome stuff. It's all natural and has been used by women in certain cultures for womanly things for a really long time.
If you can stand to drink herbal teas, just drink it three times a day, every day. If not, take capsules. It balances hormones, so that is why you might need it longer since your PMS starts so early. Or you can try drinking it only while you are having PMS - at least 3-5 cups during that.
Just be forewarned that it also can help with fertility. Since it balances hormones, it can make you more easily able to get prego. I have used it for that purpose too, and after six months of trying (not taking RRL), I took it for two weeks and ended up prego.
Good luck!