My younger sister does everything bad and is treat like an angel ? i dont understand :(?

im 15 almost 16 and i havent tried alcahol, drugs, nothing before in my life..and dont want to because of family bad experiences with all of them!! my younger sister who started smoking at 9 and is now 12 drinks and smokes and gets in trouble with the poilice, almost on an asbo, always getting expelled from school, always getting told bad things..now tonight shes walked in from a party compleatley smashed. my mum is treating her like some special kind of angel or somthing? telling her 'oh darling you should go up to bed youll feel better' both her and my dad giving my sis support and helping her into bed, get dressed, cuddles the lot!! i dont get none of that full stop, not when i achieve somthing at school or anything nothing..just nothing. Tonight all ive had is 'keep outta it!! jus stay in ya room..shes feeling 'horrible' and needs to lie down so just stay out of the way!!' basically shouting at me and stuff. I cant belive it..i dunno if im the only person who is just SHOCKED by how it is? i just cant get over it. its really upset me and made me so angry. she aint even a teenager yet!!! shes just about started puberty for *** sake! wtf? this is NOT the first time this is happend..it happens all the time. i get kinda victemised with all the situations they can find ways to do it in!! i feel like the hated child. Shes allowed to smoke , drink..do what she wants! stay out til midnight..the lottt!! only thing i can think of that ive done wrong is have and ..i used freakin protection n did it with a guy i been with for like 9 months n still with him now!!!! how can i make myself feel better about this? shes now in bed sleeping it off n got away with it yet again..:(!!