How am I(15ftm) supposed to handle this emotional whiplash?

So I am dealing with whiplash from my home situation and school.

At home I am nothing but a useless, annoying, stupid, spoiled and incompetent older sister. No matter what my younger siblings hate me and want nothing to do with me, we share a room and there is three of us including myself. My middle sister(f13) is the worst in this situation, she uses strong perfume in the room and refuses to go do it in the bathroom no mater how politely I ask and explain how it causes me migraines and sensory overload, her point is that it’s better to do in the room and that I “Have headaches not migraines! Migraines are everyday and you don’t have them everyday!”

I developed a pain condition over the extended stress I’ve delt with in school, the adults(early 40s) don’t believe it and put off sending me to the doctor to properly identify it for almost a year now, I developed this two years ago. And none of them(aside from my youngest sister(12f)) don’t use my chosen name because of reasons I neither understand or want to share.

But in school, I am bright, nice, competent and not spoiled. Teachers don’t do much to make the environment as good for me that is acceptable and accommodating but they do their best wherever they can, my classmates offer me help with my disabilities and care, hell one was offended I didn’t ask for them for help! And I am who I am without any resistance.

But I go between these everyday and the whiplash along with my other issues are messing with my head.

How do I handle this?

Tldr: people I live with think I’m a hunk of shit meanwhile everyone else doesn’t and I am confused about how to handle it