Yup - I know the feeling. My 16th and 18th birthdays weren't particularly great because I spent hours on my own, feeling like ****. Christmas is even worse - I've never liked it since my mum left and I always feel like I'm trying to be happy when I'm not. I think the reason they're so crap is because you're expecting them to be good and when they're not, it hits you worse than it would on a normal day.
I'm sorry you feel like you do
