Hey,
I have struggled in the past with my mental health too but have found that by talking to new people and exposing myself more, I've grown in confidence. Try speaking to your family and friends first because I'm sure all these feelings of self-doubt you have aren't what other people think of you. The more new people you talk to, the less it will feel. scary and daunting although I know how difficult it can be at first!
Thinking of conversation starters really helped me because they help conversations to flow better.
Try to remember people aren't as judgemental as you think they are as most people. criticise themselves more than anyone else. Everyone is unique.
Lots of love xoxo