I grew up in a big family, too. 8 of us kids, and there was always a ninth in the house. We had a little foster brother for 5 years before he was adopted and then my eldest sister had her first and brought him over for Mom to babysit. I was plunk in the middle, but didn’t fit in much better than you did. An introvert among extraverts.
Have you ever read Julia Cameron’s book The Artist’s Way? I think you’d like it.