Most Helpful Guy
For one you are not alone as I am in a similar situation as you are (overthinking things, not having much of a social life, and the anxiety). Those things have not stopped me from trying each and everyday to make progress. The best advice for not over-thinking is to not look at every action you take as a negative. I used to have a problem of dwelling on past events as "I should have did this" or "I'm missed out by not trying."
As someone who had thought like this for a while I decided that in order to combat my anxiety I had to face it head on and realize that I can't let it control my life.1
Most Helpful Girl
I used to have high anxiety and overthinking, but I got rid of it mainly with the quote
"Fake it till you make it".
This helped me get over so many hurdles especially my fear of public speaking. I often imagined myself as someone who I thought gave no shi*s in life. For eg I imagined to look at myself from the outside and I thought, 'you know what's real cute? Someone that's calm and collected' and from then on I imagined myself and spoke of myself to be 'chill' and 'laid-back'. The more you tell yourself and others this, you can trick your mind and eventually... you've faked it enough till you've eventually made it you2