Life's facts (at least my life's facts)

Today I had a mini fight with my mom. We usually have some of those. There is always something that bothers me not only of her but of everyone in my family. My sister has told me before that I think too highly of myself and that I put other people down. Although I always deny this, I think that if I'm sincere with myself, I have to agree with her. I do put people down. Sometimes I don't want to but I still do it. Is there a reason for this, maybe? I might have some psychological trauma from childhood that makes me hurt those that are closer to me. What really bugs me is that I'm totally different with other people. I would actually be considered a pushover by people outside my family. I don't really know myself. I always brag to my sisters that I know who I am and that I never have a problem with self confidence but true to be told I'm terrified of other people. Although I always say that I don't care what others think I actually do. I wish I didn't. I wish I was confident enough to trust myself and not care of what others might think of me. That might never happen. Right now, at this point of my life, I feel more lost than ever. I feel so alone. I feel like somedays I can't deal with anything or anyone. That scares me a little. Actually a lot. I don't know if I'm strong enough to have my life as I want it. I need a purpose, but I just don't know how to get one. Help!