The Anti-Plague Formula is known to be a quick cleansing formula because it will replace and remove the dead/sick cells with healthy cells. Those cells have to go somewhere - hopefully out through the normal elimination channels, but if those are blocked (i.e., liver, colon, etc.), the toxins will stay in the system and may come out when a woman has her period.
I haven't heard of garlic causing heavier periods, except for the reason above.