1) Tell everyone who asks about your lack of alcohol consumption that you are on antibiotics and can't drink. This is a bit of a cliche, so you will have to have confidence in yourself as an actress if you want to pull it off. People might still ask questions.
2) For those among us who don't feel like answering any questions about drinking behavior, it might be easier to pretend to drink! Orange juice can be "vodka and juice", and if you're drinking wine, just keep "losing your glass" or get your husband to drink for you when nobody is looking. This is probably the most effective way of avoiding suspicions, especially if your relatives know you were trying to conceive.
3) Tell everyone you have permanently given up alcohol for any number of outrageous and unbelievable reasons. You could say you have joined a sect that does not allow alcoholic beverages because they're a sin, or say that you are a recovering alcoholic and are attending AA meetings.
4) Keep yourself so busy that nobody will notice. Help out in the kitchen, do dishes, clean up after your relatives Christmas parties always create plenty of activities, and everyone else will just be really grateful you are doing the stuff nobody else wants to do. With this approach, you are unlikely to get any questions!
If you do want to let people know you are pregnant, see fun ways to announce your pregnancy during the holiday season! And keep checking back, because we will have lots of Christmas topics this month!