Karen,
I am so sorry to hear the sad news. It will be hard, esp at this time of year, but you will get through this. We lost Heather in October, but I lost my brother several years ago on Christmas eve (he was only 22), lost my grandmother right before Easter a few years ago and my daughter-in-law just had a miscarriage last night, so I am no stranger to having a loss in what should be a joyous time.
Don't even try to "be jolly" for the season. Just let the tears flow and start grieving in any way you see fit. It won't do you any good to try and put it off. But while you are grieving your loss, don't forget to also remember the happy times with your mom. You are a strong person and you will make it through this. Please accept my condolences.
Rosie