1. Most gifts are not subject to the gift tax. For example, there is usually no tax if you make a gift to your spouse or to a charity. If you make a gift to someone else, the gift tax usually does not apply until the value of the gifts you give that person exceeds the annual exclusion for the year. For 2010, the annual exclusion is $13,000. 2.
A lighter period than normal can be caused by many things, including pregnancy, stress, illness, and other things. Sometimes a woman will have spotting and think her period is about to start and not see any more bleeding. This is usually implantation bleeding that has been mistaken for a menstrual cycle.
Your lighter period is a coincidence. By the time alcohol hits your bloodstream it's not alcohol anymore, but a bunch of toxic metabolites that whiz around and give you the drunk feeling. It can't thin out your blood. Drinking *heavily* is a bad idea if you want to get pregnant (or at all, but that's another story). But an occasional cocktail is fine.