I'm really confused... Why wasn't I invited to my best friend's birthday?

My best friend and I have been besties for 10 years. We're both 15, and it was her birthday a couple of weeks ago. We had been planning something for her birthday since March. She said I was the VIP and I was the second in charge of planning, after her. We planned to go ice skating with all our friends. But it never happened and my friend never said she was doing anything for her birthday. Today, I reactivated my facebook account (after a month), and I saw lots of photos of her and all our friends ice skating for her birthday. No one said a thing to me about it. I haven't done anything wrong and nobody's treating me any different than normal... I'm really confused about this though. What should I do or say to my friend?