am i normal???? What do i do?? Sibling only!!

So i'm one of 3 girls, (im the middle) it might be middle child syndrome or something but i feel like i'm just not the eldest and everything and not the cute little youngest.

So my little sister is the thing i wanna talk about, heres some info about her in case you need it,

She's REALLY tall, taller then me
She's got some learning difficulties, nothing too bad
She always makes me feel bad about myself

I try to hang out with her but she just kicks me out and tells me to "leave her alone" and I have no IDEA how to cope with her

I try to be a good older sibling to her but because she is always being favortised my my mom she is used to getting what she wants so when i dont want to play her favourite game she would like yell at me till my mom made me leave

I don't know what to do because i've been acting a little- defensive, rude and frankly mean towards her. I WAS NEVER LIKE THIS BEFORE!!! What's happening to me???? Why am i so angry when i'm around her or even when i see her in the car or something????

WHAT DO I DO??????????????