Cut down on coffee, soda, chocolate and all junk food and keep eating small meals frequently. Fruit and such like and healthy type foods. This will help to stabilise your blood sugar and if you do this is can help PMS symptoms.
Cut down on salt intake as this and coffee can cause fluid retention and headaches. Make sure that you drink adequate amounts of water to keep well hydrated.
Evening Primrose Oil caps are good and can help.
Vitamin B6 which you run short of at the time of your period can be helpful with mood swings and other symtoms. If you get headaches try taking Feverfew tablets. These are for migraines, but are just as good for headaches and migraines with PMS. Vitamin B complex is good too. Also vitamin c can be helpful to boost your immunity. Increase your dose slightly.
If you have an upset and painful stomach then drinking Chamomile or Peppermint tea can help.
Also heat pads can help the pain too.
The herbal medicine called Willow can be quite helpful for pain too. Willow is an anti-inflammatory, but is also known as the aspirin of herbal medicine, just as Mag Phos is known as the aspirin of homeopathy.