I’m very sorry you are in so much pain. It might be that your parents think that comparing you to your sister will motivate you. It’s a common parenting mistake but it rarely works. Sadly, it makes you always anxious about what your sister is doing instead of focused on what you need to do to grow and mature.
You told me a great deal about what you don’t do. You didn’t share what you do do. You may not be interested in swimming, but I imagine you have other interests. Instead of accepting that you are second rate model of your sister, work on finding a hobby or interest or activity that is yours alone. (Then you will be “tired” too.)
Don’t compete with your sister for grades but do work with your teachers to figure out what you need to do to improve. Academics aren’t for everyone. Not everyone is a top scholar. But everyone can do well enough in school to prepare for a job or more training or schooling. I have a guess that there is a subject or two that you find interesting.
You are an individual who is valuable and lovable. Somehow the whole family has lost sight of that. Get out of you sister’s shadow so you can be seen.
I wish you well.