Hi and welcome. I've had PND with each of my 3 babies so I can understand some of what you are feeling.
Mother and baby groups can be really scary! But.... as hard as it is, do try to go because (and speaking as someone who also completely lost who "I" was/am) it is good for you and good for baby!
How old is your baby? Are you both in a safe environment? Did you get help with your PND?