How Can I Best Defend Myself Against Self Doubt?

I am also attempting this, so I can't say this surely works but I do think it's getting easier. Change your thoughts. When you catch yourself thinking something negative ask yourself what purpose the negative thought is serving and if it is necessary. Pay more attention to the positive and recognize your accomplishments. Perhaps applaud yourself every time you step out into the world even if it's only for a little while at first. If you google 'cognitive therapy' you might find more tips like these. Good luck!