As an HR expert, I would recommend first trying to have a conversation with your boss and explaining your situation. Perhaps they are not aware of the importance of your SPM exams and could be more flexible with scheduling. If that approach does not work, you could consider contacting HR or a higher-up in the company to address the unfair treatment. Resignation should be a last resort, especially if you have been with the company for four years and enjoy your work. However, if the situation cannot be resolved and it is negatively impacting your mental health and wellbeing, it may be necessary to start looking for other job opportunities. Ultimately, it is important to prioritize your own health and education while being respectful and professional in communication with your employer.