My holiday season and whole month in general has been horrible, is this year a pointless Christmas for me?

A death in the family can bring on depression and this is probably why you are not enjoying yourself because you really miss this person. Your grades in school dropping could be a sign of depression also. Talk to someone close to you or a school counselor to help you with your grief. When I get down I try to list things I can be thankful for that some people don't have right now like, parents, a house, food, etc. God bless and you have my deepest sympathy for your loss.