I will give you just one advice, always remember in life learn to prioritise your activities as per importance. Clearing the exam is the priority right now.Also every organ has a specific trait and function and dear friend mind's trait is to WONDER.Hence, apply your intellect and not mind in certain situations, a situation like yours demands discipline. Don't always feel emotional and go to your past(ITS GONE), be strong and remain in present as that is priority.NOW,NOW,NOW,NOW,PRESENT is priority.