What happens it is actually that you retain water and you bloat before your period. Personally, I put up to 3-4 pounds before my period, and I get rid of them after the 3rd or 4th day in my period.
After the second day you should not crave sweets anymore and you should feel already better. Your body has already eliminated most of the toxins so, yes, it looks easier to lose weight then. It works for me. But keep in mind that not feeding yourself properly during this time and cutting down all food can bring down your Calcium and Magnezium (and not only), can make you feel weak and sick, can make you feel sleepy and lacking energy. If this happens, you will most likely slow down your metabolism and your fat burning will also decrease.
So keep yourself hydrated and eat plenty of veggies and good calories. The days right after your period ends are the best, from all points of view, for losing weight and exercising.