I just wanted to hold your hand, virtually.
I understand how you feel. Loneliness is a terrible thing. I don't think many people actually know what it is like to spend long stretches of time by yourself. It messes with you head, it destroys your mood, it makes you feel worthless. There is a reason why solitary confinement is used as a kind of torture - because even strong people can be broken by isolation.
I don't think this is the kind of problem that can be solved in one fell swoop. But it is a problem that can be tackled in chunks. The first step is quite literally a step - outside of your own front door. A walk in which you are forced to interact with someone - just a stranger, a shop assistant, a cashier - do it right now. There's something about moving gently in the fresh air, in allowing your eyes to see beyond the distance of an interior, that is helpful.
I do think joining a group is a GREAT idea. There must be something you've always wanted to do. Come on, now, admit it - you'd love to windsurf/make pottery/learn to book patisserie/take a night class in rocket science or TS Eliot/learn the samba, or karate. Sign up to a class that's close by where you live, and GO. It won't necessarily be easy the first few weeks, but persist and you will soon meet new people.
Your confidence sounds like it has hit rock bottom, too. A book like Feel the Fear and Do It Anyway might help. And I definitely second those saying to revisit your GP - it make be that different ADs, or an altered dose, will help.
Hand-holding here with you.