I can't do this anymore

So this is gonna be a long story (sorry about that)

So I have never felt like I "belonged" in my moms house. My parents had split up when I was only six and my dad disappeared for almost three years. When my dad came back I was ecstatic but my mom wasn't. So they fought for custody and asked me what I wanted and at the time I wanted to live with my mother and visit my father. Now that I'm older and 15 I have a different point of view. My mothers house is horrible. And yes we have normal family bickering and such but it's not about normal thing like can I go out or why can't I wear this dress. It's about that I take to long in the shower and that I eat to much and that I drink to much( juice and water) and that I use to much electricity and that I am disrespectful. Now sometimes yes I can be a tad disrespectful I will admit that but most of the time I'm just fighting for normal human rights. Like going to the bathroom when I need to, having a key to my house so I can get in if need be or being able to go on a walk when my anxiety, depression, or PTSD are getting bad or being allowed to brush my teeth for as long as I need to. Now recently that stuff has still been happening (which I can deal with) but also more stuff has been happening. My older sister had to move into my moms house because her baby daddy got abusive and is now in jail. Now my parents and me have done a lot for my sister under one condition, that she doesn't go back to him and recently she has been talking to her friends about going back with him. Now that is wrong all on its own and I'm telling you this so you understand where I stand. My sister dropped out of high school did drugs and still does while she is pregnant she works at turkey hill she is living in my room and keeps spending money on fake hair pieces instead of putting it away so she can get out of the house. Now my little sister is young and doesn't do much besides play in her iPad and talk back to my mom and step dad. But guess what I do have a 3.8 GPA am an honers student I'm even ahead a year in math so I take the next grades math I am still in school I follow the rules listen to them don't go to party's don't do drugs and try not argue or be a bother. But guess who gets yelled at and belittled all day and night long. On another note I stayed most of the summer at my dads house and have been chilling in piece and quiet and getting to eat when I'm hungry use the bathroom when I need to you know basic things and I also haven't been yelled at and screamed at for every little thing that I do. My mother even said that while I was at my dads house that she doesn't have to do anything for me like take me to appointment that are set for days that she's off but my dads at work and somehow she wants him to be in two places at once but when I'm at her house Dad has to do this and this and this. That just isn't logical to me but whatever. Now back to the room situation so my sister is staying in my room with her baby and she's pregnant. So she has rearranged my entire room taken my stuff off of my desks and even taken my stuff out of my draws but whatever it's fine. So I stay quiet and deal with it but my sister wants me to do this and do this when it's my room but you know what whatever I'll stay quiet and do what she wants. Then my mother also wants me to take care of my niece. Now I live my niece to death and love to watch her I just don't like how there using me. It's like they only love me and want me around when they can use me to do this or get this but when I'm not useful they shit on me all day. I have been at my moms house since six pm yesterday and it's four am today and I'm already going crazy. My suicidal thoughts are coming back my self harming thoughts are coming back I've had to start taking my meds again and on top of that there were two people who I loved more than anything and now there gone too. Basically I just don't know what to do. I go to school at the school near my moms house but I can't live here anymore it is too much for me I'm to stressed and depressed and anxious here but I can't go to my dads house cause the schools near him aren't good schools and I'm too young to drive myself to school and I don't have anyone to drive me. I'm thinking about running away or even killing myself because I can't take it anymore. Everyone keeps using and hurting me and I'm forced to sit still and be quiet. I'm just so done with everyone's bullshit and not being allowed to anything. I'm 15 I should be able to eat and shit when I need to. I just need advice.

Update: I thought out of all people my dad would understand but he just called yelling at me because he's getting a call at work from my sister about me. I didn't tell her to call him but it's my fault that I couldn't sleep up stairs because she wanted to put the tv super loud. And apparently me telling her that I can't sleep like that is me being selfish because the baby needs the tv super loud in the morning. So I went downstairs to sleep on the couch so I could sleep but guess what I'm doing something wrong again. Instead of me yelling and screaming at my sister I went downstairs so she could do what she pleases with my room but I'm still doing something wrong. No one cares about me. Or what goes on in my head or in my heart. I'm literally breaking right in front of them and they don't seem to care. I understand the baby comes first but you don't just start treating someone like gum on the bottom of your shoe. It's like if I don't exist and when I do it's just to be yelled at. If I'm here only for that then why am I here at all. I have decided I am going to kill my self or run away I just don't know when.