Why am I always excluded?

I just had a big performance tonight that was supposed to be fun. All of my friends would be right next to me singing. However, I would wander around trying to figure out where they were. When I did, I attempted to join into their conversations and activities. But, I would always be left out and standing alone in the end. I don’t know why I feel so lonely. I probably am overreacting and should just move on, but I can’t when it happens every day and I don’t know what to do.