It depends. Sometimes it's my age - I just feel OLD and thus this percieved lack of authority, especially as a woman - that's a whole thing you dont need to worry about. And it depends on the situation - I'm never confident with strangers or at parties. I do put on a confident face though - no one actually believes I'm not confident at all! I'm very good at pretending - you have to be, as a teacher.
Nah, as a foreigner it is something I have to worry about too. Different - but similar.
I have this too. I believe that "introvert" is a role people play. They can play extravert too.