Everyone always has something bad to say about me!?

I'm 13, my mom makes faces at me when she thinks I make faces at her, she calls my voice a pterodactyl voice. My younger bother has AD-HD, so when we get into a fight it's automatically my fault. I have 2 brothers and 1 sister. My brother is going off to collage so my parents don't even bother when he's around, my sister is 15 and has her own life. My mom picks on me and my sister, her favorite line, "you guy's are getting chubby". But everyone except my dad picks on me. My brothers, my mom and my sister, I am the easiest target for them cause I usually don't retaliate. But the problem is, every night I look in the mirror and cry cause I know I am not pretty, I have never had a boy friend and I only have one guy friend, most of the other guys ignore me or just say "hi" down the hall but some mock me because I have buck teeth, (not big, very small), and I want to go run in the bathroom and cry but I don't and I suck it up. I need some advice.HELP!!!