GC -- I don't know how specifically a therapist can help with social anxiety except perhaps to help you check your perception of how people receive you?

So, if I tell Blondie that X, Y or Z reacted in this way to me and I'll invariably pick the worst possible reason for why they did so, she'll give alternative explanations and more than a few times, I've found that she's been right and I'd just jumped to the worst motive kinda thing.

Btw, I just read this piece by NYMag's advice columnist, Heather Havrilesky writing in response to a reader and it really resonates (Warning: If you click to the article, it's got trigger-y stuff in the question sent by the reader):

Being what you are looks like this: You enter every room as a calm, neutral observer. You are average. You don’t have an agenda. Your only job is to listen and observe and offer your support. Your only job is to watch and learn and allow room for yourself, even when you don’t say a word, even when you don’t look that good, even when you seem useless. There you are, giving yourself the right to be without running or hiding or dancing. That is grace. It matters.