Why Does My Hand Trembles While Trying To Write?

I'm 23 years old. I cannot write fluently. my hand trembles. and I m unable to take my exams. Only my writing is readable when I write very slowly and holding pen firmly. But then I cannot complete my exam in time and also my hand get tired.I face this problem only when I write. Please help if I can get instant relief for 3 exam hours or permanent relief.