Hi mei ting,
stress is part and parcel of life. Fortunately, as a student,
there are many ways to reduce it.
For O levels, the easiest way to have less stress is to know
what you are doing, have your own strategy to scoring. Set a
target, have a goal, know what you are working towards.
When you are clear in your mind what you really want to achieve,
and your strategy towards achieving it, you will be happier, be
more effective, do better, and all these will have the effect of
making you less stress.
Here are some articles for your reading.
Habits of Effective Students
Physics in a Nutshell for Os and As
The Principles of Academic Success
Ganbatte!