I have been advised not to fast because of the excessive heat and due to us having to write exams.

Answer

The persons who say that you should not fast because of the heat and exams are agents of shaitaan. It is haraam and a great sin not to fast. It is better to abstain from the exams and fail rather than not to fast. The Qur'aan says that the heat of Jahannam is hotter. The advice is the advice of munaafiqeen.