The Philosophy of Cognitive Behavioural Therapy: Stoic Philosophy as Rational and Cognitive Psychotherapy by Donald Robertson
CBT is the only modern day psychotherapy that is based on empirical evidence.
From the FAQ:
Stoicism and the Art of Happiness and How to Think Like a Roman Emperor by Donald Robertson are both practical, readable introductions to Stoicism intended for modern practice, readable independent of historical sources, combing selected elements of Stoic theory with exercises inspired by Stoicism and supplemented by techniques and developments from modern psychiatric therapies. Art of Happiness presents theory and exercises in the style of modern "self-help" book, while Emperor is structured around a biography of Marcus Aurelius, in which Stoic theory and exercises are presented as digressions. The content of the two overlap significantly, although the first places more emphasis on the theory, and the second, history.
Well, as a moderate sufferer of social anxiety, I will say you can make it better. You might look into books by Donald Robertson such as :
https://www.amazon.com/Philosophy-Cognitive-Behavioural-Therapy-Psychotherapy/dp/1855757567
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I don't take your age for granted here, you may feel old for your age, but mostly acknowledge the anxious thoughts, tell yourself that they are only your opinion of the situation and not necessarily what is happening.
I initially followed the principles of Stoicism, which is a philosophy that's very close to the principles of CBT. So my first resource was /r/Stoicism, where you can find things like this and this that have direct correlation with CBT principles. Greek and Roman literature might be hard to get into, but there are very readable translations and the principles are applicable.
Of course, not everyone is interested in philosophy, so my recommendation would be to find something along the lines of Judith Beck's Cognitive Therapy, or other similar resources that are based on research. I can't really recommend else because I haven't read much from other authors.
But in general I would recommend reading about cognitive biases in general, along the lines of this, this, this, or this. Being conscious of how everybody thinks might help you see some negative spirals in your life, and can help you change the environment that might lead you to that negativity.
But again, professional help can be very useful, so definitely consult a professional who is maybe better for you. Good luck!