What do you do when you never had confidence when you were young and still don't have confidence as an adult?

Do things to give yourself confidence like sticking at things and succeeding in them. Work out, keep doing things you're interested in and you'll naturally get good at them and have more sources of confidence. Realise that everyone else is just another person who holds no more value than you do and what you interact with is just the social faces of others, they won't show you their insecurities so don't compare yourself.