Dear Anna,
Everything goes smoothly with me. Thanks.
I extremely understand how you feel. It's normal for teenagers to have problems. Here are some suggestions.
For the first problem, why not ask your parents to cut down a few of the after-school lessons? Also, plan your time well and make the best use of your time, so that you can balance study and free-time activities.
As for the stress, you can tell your parents about your efforts and ask them to encourage you. What about explaining that you will keep trying? I think they will understand you. You should also take exams seriously, put in more efforts, go over your lessons and ask questions if necessary to improve grades.
When it comes to the problem that your parents argue a lot, you can ask them to calm down and find out the reasons for their arguments. Try to show how they are important to each other, ask them to have an understanding communication so that they can get on well with each other. Then your family will be peaceful.
Talking about the problem that your sister looks through your things, you'd better tell her it's not right and that it makes you angry. You can tell her to ask for your permission next time.
Sharing a problem is halfway to solving it. If you still feel stressed, listening to music, reading books and doing sports are also excellent ways to reduce your stress.
Problems are everywhere. Let's be positive and smile to life.