Fed up of being treated differently from my sisters. ?

Its coming up for my 18th birthday, and my mum has decided i cant have a party. Yet my TWIN sister is allowed one, how is this fair? Shes allowed to go out drinking and staying at her mates more than me too. Ive always been treated differently than my 3 sisters, when i was a child i was diagnosised with DCD and dsypraxia. So i was more clumsy and had trouble with speach and coordination bt now im not as good at sports as most bt people cant tell and i dont fall over alot. Yet my mum still treats me differently. Last year i got so fed up of being treated differently i tried to kill myself. I self harm cause i get upset from being treated differently. I spoke to my old shrinks and they all said my mum has reason to treat me differently cause i tried to kill myself. Whenever i try and tell them that its been happening longer than that they dont listen.. I seriously dont know what to do anymore just want outta the house and never to see my family again.. Any advise?