I just had this experience in person with support group today, I just didn't know what to say! I am not a big talker unless I have something specific to say. Maybe you are the same way? All I have to say is yes it is awkward to be in a group and not know how to begin. I look at myself through those really dark lenses too sometimes. Just remember, something you have to say may really make a difference for someone. Never be afraid to speak out!
edit to add:
Oh yeah and your "don't know how to talk about myself" really struck a chord for me. I think the really sucky thing about therapy and support sometimes is that we are talking about ourselves in a negative light. Yes it is insight but we're not talking about our passions or hobbies, therapy is not entirely "talking about ourselves," it's often talking about our worst, scariest, selves. It is hard to articulate this depressing stuff about ourselves sometimes, and can feel a bit self indulgent. So.= anyhow, there's my 2 page response to your query I guess.

Good luck!!!!!