Hello Friend, Good that you are seeking a help here. Such lack of interest, laziness, negativity,dullness etc are symptoms of Anxiety. Your stree around exam preparation or fear about exams may be  causing such depression. First you need to change your mindset and fix some goal or milestone. You may need a professional guidance through a counseling support to understand the real root cause for such negativity and possible solutions to overcome.

You have to get in touch with good psychologist, who could identify your challenges and diagnose the illness.