For many suffering with OCD, holidays tend to cause a flare in obsessive unpleasant thoughts or compulsive behaviors.
It's not the holiday in itself, but the variety of things that come with the holidays. For each person it can be a different trigger. For example, the pressure to be in a happy mood. Stress from meal preparation or from the anticipation of seeing relatives or people not seen in a long time. More crowds in stores. Loneliness during a time of year that radiates the gathering of family and friends.
Whatever the reason, realize it is temporary and will pass. If you will be alone, plan things you enjoy doing, even if they are at home. Do something special for yourself. A culinary treat. A favorite DVD. A long warm soak in the bath. It doesn't have to be a big thing. Little celebrations are the gems of life.
Having OCD doesn't make for a bad, abnormal, or crazy person. A person with OCD can do the same things other people without it can do. And that includes having a pleasant happy Thanksgiving.