The cravings a week before your TOM are due to low serotonin levels. Low serotonin is caused by low estrogen, which is why you crave carbs.
Be "diligent" about what you eat. Feed your body whole grains and healthy carbs and you'll be surprised that the cravings can be satisfied with normal portions. Eat sugars and refined carbs and you're going to find yourself even worse off (blood sugar spikes and crashes will worsen the cycle).
If your PMS is REALLY
bad then think about picking up a natural progesterone cream and using that the two weeks before your period. It can make a world of difference. Check out the work of Dr. John Lee or at least the articles on his website: http://www.johnleemd.com/
If you're on BC pills then it could be suppressing ovulation which would could impact your progesterone levels.