I didn't reply before because I have been living a similar situation to yours those days. How were I be able to tell something with sense when I was feeling so overwhelmed?

I can figure out the situation you describe being at school a year before your sister.

My anxiety also makes me doing things much worse than I'm able.

Please, try to avoid as much as you can, comparing with others. Set your dreams, your goals to achieve them ( each step to get to them) and don't let anything ( neither your mind) appart yourself from your path. Compare you with yourself, the popuri before and the present popuri.

I have two siblings. I'm the oldest one and however I'm the weakling. This is how I call myself bc it's the true. But...the relevant is keep going to be better for others and myself. All of us, are different.