Im sorry about your sister being so horrible I know what its like I had my sister tell me all my life that I was thick fat & ugly I know now that she was jeluse as I was the skinny one & she was the fat one but she is the reason nI have anorexia I would talk to her & tell her that as she already knows you are under weight & tell her how you fell about your self & what she says to you is hurting you & hopefully she will stop if she doesnt then tell your mum I hope you can get it sorted out its not nice to go through at any age im 29 & 121lb & she still thinks like that about me she is 31 & about 170lb

Take care