My brother is so mean to me ?

I'm 12, and he's 14 . He always calls me fat and retarded and that I'm a SPED and stuff like that. He's bigger than me and can beat me in an arm wrestle with tree fingers. I'm around 172 cm. My brother might not be A LOT bigger but he can hurt me 100x more I can hurt him. He doesn't care about me, if I say his name, he says shut up or piss off, if I get bashed at school, he'd say, what a , learn to fight you d***head. My mum says that we are brothers and we fight, she doesn't really care if we argue, she just splits us apart if it gets bad. My brother has punched my stomach in public infront of his friends to make them laugh, he's thrown a plate at me and it cracked and I stepped on it and my feet were bleeding , he nearly drowned me in the swimming pool for fun and he always does the same thing. He gets in trouble everyday and says I won't do it again but does it again. I think he'd rather see me hurt than him getting in trouble. Please help ? :/