For years I have had a problem being in large groups. Because of my cognitive difficulties, I have issue with the noise, as I can't keep up with all the activity and conversation. The article I've provided the link to below gives some explanation for this.
I pulled one paragraph out, as it states what I feel so much better than I might be able to do.
"I am unable to carry on a conversation at a party or at a dinner where there are other people talking, as I cannot maintain any sort of attention span for either what the other person is saying or how I can respond in a normal manner."
At large gatherings I tend to sit off to the side, watching more than participating, enjoying one to one side conversations.
For years I have had people think I am angry, or annoyed, because they see, not quite a grimace, but definitely a furrowed brow that they read as anger. It actually means I'm concentrating, trying to keep track of what is going on. There's mention of this in the article, too.
It's worth a read.