I was diagnosed with expression language disorder when I was in pre school. I'm not totally sure if this is still true to this day. I am generally quiet mostly because I'm usually processing and listening more than speaking. There are times when I can talk quite a bit... all depends on my comfort level of the person I'm with and topic.
Every single human being has a disorder. It's called the sinful human nature.
When I look at my childhood (which is not often), I appear to be a total, anti social, introvert. Some of it was environmental. By the time I was 16, in ten years I had lived in 14 places and I was in my fourth country.
I read a book by Tim LaHaye about the four temperaments. I identified myself as melancholic. It's not a disorder, it's my nature. For example, the book says to identify your weaknesses and strengths. It was easy for me. I had no strengths as far as was concerned.
You sound very much like me. God has drawn me out of my shell over the decades. I was able to speak at a secular conference in front of around 300 people. The Lord had set me free from self consciousness to that degree.
Somehow every problem that a person suffers has become a disorder. Everyone gets a label. This is handy for psychologists as they can charge 60 bucks an hour to try and fix the "disorder."
Jesus came to fix "disorders". He does it for free because He loves us! I'm a different person now. That's not my evaluation, but friends who have known me for 30 years or so.