Dear:
I so sorry to hear that you feel rather neverous whenever you are taking any important exams.so I will offer you some tips.
Frist,It is important to have a right altitude in the exam.Most of us have such bad times.So don't worry much about it.You should keep relaxed.Second,If you study hard and make careful plans for every eaxms.You can be more confident.Finally,you can do some outdoors excersices for relaxing.
I hope you will find my suggestion is helpful.