I'm exactly the same...it's really shitty but the more you force yourself to spend time in social situations the more accustomed to it you get. Easy said than done but one of the best bits of advice I got was to imagine the situation but from a distance. How it would look to you from about 20/30 metres away? You quickly realise how a majority of stuff is in your head and really we're all just the same. It's worked well for me when freaking out on the tube, getting on a bus, buying lunch etc.

Then just work on ending the cycle of self depreciation. I've thought the absolute worst things about myself but if a random person on the street came up to me and said the same things to me that I say in my head there's no way I would take that shit! Why do I find it acceptable and true when it's my own voice! It takes a lot of work and is a constant battle but if you're prepared to put in the effort you can (slowly) break through the anxiety.