Sounds like your brain, like most folks, is exeriencing a dip in serotonin around that time. SImple carbs temporarily cause a surge in serotonin levels, which is which folks tend to want them when they're menstruating or just feeling sad.

I don't know what to tell you. You don't want to start taking an SSRI (prozac, paxil, zoloft, etc.) just for this intermittent problem.

You could try doing something else to stabilize your mood. Exercise works extremely well -- but I find that I have to do it several times a day if I'm really in a funk.

You could also try to find a LC snack that you can "binge" on without interruption for the duration of that time. I think it's risky to eat the Atkins fake-sweet (shakes & bars) because they can just make those cravings more persistent. Is there anything else you can substitute for your carb fix?