Dear , you know who you are and what is your capacity and ability. You know the more you try and work hard, the more you will be able score high marks. Please stop apprehension. Never relate your performance with change in school. There are no relations. There is only one factor. You are not getting good marks because you are not preparing well or you are anxious about the exams. You may see a psychologist
for counseling. Alternatively you may opt for a motivation therapy. Take care.