Hi. I've also suffered severe and persistant bullying at school, and then in my previous job/s, so I can very much relate.
Your problem is something. What you've endured is traumatic, is abuse. Yes, bullying is abuse.
What is happening in the group now probably is magnified by what happened to you at school. Triggers seem so so huge and frightening. The sad fact is that once you've been a victim of bullying, the risk of it happening again is increased, and it tends to become self-perpetuating too, I know myself that I have an internal bully who bullies me, the way They all did, Back Then.
Adult Bullying by Peter Randall is an excellent book that should help. I'm not sure what to advise about what you're suffering now, as I've managed to get out of the bullying environment I was in [primary school teaching.] and build a safe environment for myself, at home and work. I am still vulnerable to the bully inside, flashbacks and dissociative episodes, however and they are my working points.