Instead of beating yourself up for not being positive, just celebrate being the wonderful you exactly as you are! Trying to be positive is doomed to failure, because it implies you are lacking and not good enough. Try being loving, kind and non judgemental, first to yourself, then to others. You have everything you need within. Those negative, sad thoughts come and they go. They are just thoughts. Don't chase them.
Happy New Year! All you have to do is be the beautiful you! Relax!