Social anxiety in a 13-year-old boy

Hey folks, I am turning to you again for advice with my son who is going to turn 13 in a couple weeks. Over the years I have posted about his difficulty with social skills and gotten some good advice. We had him in therapy for his anxiety, which he hated, but he did read a book that was suggested here.  He may be on the mild end of the spectrum, but has never had formal testing . The trouble is, he just won’t join any groups. Meaning that even if he knows a few of the kids in a larger  he won’t go over and hang out with them or talk to them at all.  This even goes for sports teams where he has had months to get to know his teammates.  He even goes so far as to sit at a separate table, all by himself while the other kids are all chattering happily away at the next table over . when I ask him about it He says he doesn’t want to be awkward. I told him buddy I’m sorry, but you sitting alone and isolating yourself is pretty awkward already.  Thankfully, he has two friends, but at school or in a larger peer group he barely interacts with them. It’s almost as if he’s scared when other kids are around. I’m pretty sure this is social anxiety. Has anyone had any luck with meds? I remember one parent posting about a low dose of Lexapro, helping her child . We haven’t really considered these because we were afraid of the side effects. He had individual psychotherapy for a while for his phobias, but he hated it so much! We have looked  around for peer social skills groups, but haven’t had any luck. We are in the  North Bay, but willing to do online groups or whatever.