First of all, think about whether something has influenced you recently, whether it's your own business or family business, or the deep things and behaviors of a classmate around you, and then block it out.
Secondly, it may be that your goal is in a vague state. You can find a notebook to carefully write down your original postgraduate entrance examination goals and remind yourself.
Third, lack of motivation, we should find a spiritual pillar, or find a competitor to move on.
Wish you success!