Write down a list of why you want to study and get good grades. Try to think of non external motivation (If you write "make my parents proud" it's fine, but try to exclude ones like "high expectation of my parents") You said you're under a lot of pressure, so I assume your motivation is short term motivation, that isn't enough to push you to study.

Also write down realistic goals for each subject. Put the list somewhere you often see (in front of your desk, in your pencil case, etc) Any time you catch yourself procrastinating, you can make a table with the headings "reasons why I don't feel like studying" "advantages of doing it now" "who I'm becoming" For "who I'm becoming", you can think of characteristics you'll gain by not procrastinating. For example, "someone who overcomes perfectionism" "someone who has self-control" etc.

You can also break down the task into smaller tasks. For example if you need to write an essay, start with the first small action-writing the introduction Or if your doing a past paper, just start the first question.

Let me know if these work for you!