I've often thought I have it but I've learned to avoid things less, and for me I think it's more depression, anxiety, and prior trauma that causes my poor self-esteem than a personality disorder. But the older I get and more I read up on this stuff, I feel like it's less like distinct things and more like a bunch of overlapping Venn diagrams, and in the end the treatment for these things is often the same either way. Lots of therapy, which means finding the right therapist and then exploring the right approach for handling problems.

As far as I can tell, the thing that distinguishes AVPD is that it's a personality disorder, which has to meet a bunch of criteria (persistent, inflexible, not the result of trauma or another disorder, etc.) so it's more difficult to mitigate.

As for how to mitigate it, what works for my social anxiety is the usual recommendations: box breathing (breathe in 4 seconds, hold it 4 seconds, out 4, hold 4, repeat) to slow your heart rate. The 4/5 R's on handling obsessive/intrusive thoughts (recognize it's happening, relabel it as unwanted/delusional/intrusive/whatever label is helpful, reattribute to symptoms of your mental illness, refocus your task/thinking, reappraise the thought later when you are in a safe place). Learning to just stop thinking. Learning patience and being kind to yourself. I hope you can find some peace, and find the right people to bring into your life. I know loneliness very well. A deep longing ache inside that waxes and wanes but never really leaves. It hurts and I'm sorry you have to deal with it.