Firstly, welcome to the community!
I nearly started sweating myself reading all the obligations and responsibilities you have to keep up with. It’s no wonder you’re stressed, it’s a perfectly valid emotion. I was reading your part about your weight fluctuations. This happened to me because I of the amount of anti-depressants I was and weight gain in a common side effect. Like you this was happening whilst I was studying and I turned to unhealthy dieting methods. Biggest mistake of my life. Why? It impacted my metabolism because I want giving my body the nutrients it needed. I stopped and then after a traumatic experience I gained weight so I turned to the unhealthy dieting methods again. This time I experienced a lot of side effects like hair loss, headaches, light headedness and after discussion with my psychiatrist I realised this wasn’t sustainable.
So I ended up on the tried and tested approach of just healthy eating and balancing that with exercise. With everything going on in your life I imagine you’d be really burnt out so take baby steps. Like maybe take a walk just on your street for 10 mins when you have time and keep building on it. Like @fishyie sais with so much focus on perfection and that me standard of beauty it’s hard to remember humans by nature are flawed and there is nothing wrong with the that. I hope you’re taking care of yourself and wish you all the best. Year 11 can be stressful but if you balance your emotional, physiological and psychological health it makes the ride a little less daunting.
Take care and I hope to see you around 💜