Im writing exams and feel stressed, what can i take to calm myself ?

You are smart: to want to get a handle on this. It sounds like you have already begun to identify what triggers stress--some conditions at school. Often simple things add: commuting,balancing school/work. Focus on eliminating the triggers first. Then the lifestyle basics: healthy eating, exercise, sleep. From there I advise Mindfulness Meditation, deep breathing, Yoga, massage. Read up on these. Best wishes