Looking Withdrawn in Social Situations?

When I am in social situations I have the tendency to freeze up and go quiet, and according to some people I look/seem withdrawn (like am thinking elsewhere). I must admit that when im in these social situations I focus on the myself (i.e. Whether I look ok, what are people thinking of me, do I look withdrawn now, are they noticing how quiet I am etc) probably the reason why I look withdrawn as I dont focus on, what the people are saying to me or anything, am focusing on what i should say to people and how I am being percieved by them.

Another reason I stay quiet is because when I do try to socialise my voice goes very quiet, people sometimes struggle to hear what I say because of it which makes it a bit difficult to build good rapport and also puts me off trying to make conversation with people.

This makes me realise, that this is a major whole in my game, as HB's and friends alike will just percieve you as weak/weirdo or as one of the sisters of a HB i met said "your a nice guy, but your too quiet and you look withdrawn - I told my sister I think your no good for her" and "your a nice guy but there's something I dont like about you - your too withdrawn its like your thinking elsewhere". These comments are so debilitating and becoming too much of an often thing, I need to get over this and would appreciate some advice or recommendations to do so?

Is there any way you can shape your voice so you can still project it loudly and confident enough for people to hear? How can I stop feeling or looking withdrawn in these social situations?