Need help with my stepmom issues?

Okay. So I just moved in with my dad, stepmom, brother and sister in July. The first time I met my dad was Summer 2009. I went and visited him over spring break last year and I loved it. I was having really bad problems at home, and decided I needed to live with him if I wanted to ever become somebody in the world. So I did. At first. It was AWESOME. I loved it. But now, my stepmom goes through my room, she goes through my make-up and takes whatever she likes, she uses MY razor to shave HER body(thats just disgusting), she tells EVERYONE that I'm on birth control and that I may be moody because of it, my dad is 3/4 deaf and she'll disagree with what he's saying and get mad and talk bad about him under her breath so she knows he can't hear her. I've told my dad that I have problems with her. And he says they're over "petty" things, but I've never told him that she talks bad about him under her breath. When they fight she blames me for the reason they're marriage is starting to fail. She just EXPECTS me watch my little brother and sister all the time! I'm fine with it once in awhile, but like ALL the time. And she's constantly lying to my face. And I know some of the things she lies about are petty, but added up it's ALOT. Do you think I'm being petty? Or do you think I have a legit reason not to like her?