What to do? i feel like my head is going to explode?

i feel like my family is going to push me over the edge. where do i start. i have depression, i think i have anxiety and post traumatic stress disorder, i have depersonalization, i'm stressing about a lot of things right now. around this time last year began the worst year of my life. my parents started smoking again, my beloved dog got rage syndrome and occasionally attacked us but it didn't get serious until he bit my brother's face and we had to put him down. we tried to help him as best as we could and got him dog psychiatrists but nothing worked. i loved him so much, he was my best friend and one of my only friends. before i got him i was depressed mainly i think from heredity and because i'm home schooled and only have one best friend who i never see because she goes to private school and has a lot of school work and never has time and we don't live that close to each other. after i got my dog, i wasn't really depressed anymore, but after we put him down i guess i was just in shock and everyone was crying so i felt like i needed to be strong and i didn't cry. well then my sister went through a rough patch where she went out with this guy and she fell in love with him in the first two weeks (they only went out for a month) and when he broke it off she was devastated. it wasn't easy for me to watch and i have very sensitive emotions so even just being around someone who has a negative energy about them can ruin my day and make me depressed. she also got accused of cheating in one of her classes in college and the teacher didn't have any proof and she got it put on her record. she got fired from her job for something she didn't even know was wrong. i began to get depressed again and no one knew but me. eventually i started having emotional breakdowns and even cut once and had thoughts of suicide even though i didn't have any plans to end it. i told my best friend and she started helping me through it as much as she could, but she couldn't help much because she was so busy and we never see each other. eventually i got up the courage to tell my mom and after 2 months of begging my parents to send me to public school they said they would. that helped and since then i haven't been as depressed but i still have a lot i'm going through. i went in for my annual physical and the doctor recommended that i see a counselor and gave me a list of them in the area, but my parents refuse to let me see one. my relationship with my sister (she's 21, i'm 16) is terrible, ever since she started hanging out with this girl she treats me like i'm unimportant and is really mean. once she started asking me about my problems and i told her and opened up to her and she laughed in my face an treated me like i'm pathetic and small. she also told me multiple times that when i go to school this fall i will fail all my classes and everyone will hate me and i will come home crying every day begging to be home schooled again. i know what i'm getting myself into when it comes to school, trust me. and she just treats me coldly when she's around me, and keeps trying to get me in trouble and just bitches about her oh so terrible life all the time, but her life has gotten better since last year i can tell you that. she shouldn't be complaining, most of her problems are fake drama things that she makes happen herself, just so her and her friend have something to entertain them. whenever my sister is around my mom, my mom becomes sort of like her and treats me different then when it's just me and my mom. she treats me coldly. the only one who treats me right all the time is my brother who is 19. we've been so close ever since i was born. my parents constantly tell me to get a job and treat me like i'm mooching off of them, when my 21 year old sister is living at home rent free, driving their car, eating their food,etc. and doing whatever the f*ck she wants, walking around like she owns the place and treating me like crap. and now my parents told me that if i take the placement tests for my high school and i'm behind then they are keeping me home schooled, but i haven't learned crap since i was 10 because my mom used to teach me and she did a good job, but then she add to go back to work when i was 10 and since then i've had to teach myself, which i know i lack the discipline to do. i can't stay home schooled any longer, it is responsible for most of the problems i have. i'm afraid if i stay home schooled i will end up getting so depressed i kill myself. i am just so stressed right now and i don't know what to do. i know i need to study hard so i do alright on the placement tests, but that's all i know. i know i have to go to school because that is the only way to get away from my problems. to get out of my parents control. please help i just don't know what to do and therapy isn't an option. please help me.