Is this caused by the lack of time alone/time for myself (pls help)?

i'm 17 y. o and i live with my family including my twin sister, who has always been close to me. we share one room, so i'm with her 24/7. only place where we're separated is school, because we go to different schools. 1 week ago she had been on a trip with her class, so i was home alone whole week and i realized something. i'll tell you a backstory:
i'm not very social and i'm sure it's because i don't feel like needing any social interactions beside spending time with my sister. that's why i don't have any friends in school. when i try to initiate some conversation, it's forced and then awkward, because deep inside i don't feel like talking to anyone - because my social battery is low. and then i don't have friends (or i have some just for a while). BUT. the week when she was away from me, i had so much time alone in my room, so every time i went to school, my social battery was full. i've made some new friends and i was so confident that i could talk to almost anyone i liked.
but why is my social battery low (now when she's back)? because i'm always and everywhere with my sister. because i don't have any time alone just for myself.
i tried to explain this to her, but nothing changed and things in school have just got worse. now i'm losing my friends again and i'm so unhappy.
i would be so glad if you gave me any advices how to solve this. i'm really hopeless.
Is this caused by the lack of time alone/time for myself (pls help)?
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