Missed his school. Of misunderstanding!

My nephew purvansh 13 years old student of 8th class from last 2 years his education result continuous falling. Due to falling of result we had change his school,but he went school 2 days n after that He is afraid to go to school, n creating lot of misunderstanding regarding health issues like vomiting,stomach pain,gidding. N showing abnormal behaviour to go to school. We had consulted his class teacher and principal regarding this type of behavior but they had said there is no issues with this school.now the child is demanding change his school and take new addmition in another school which is near by home. Now again the child showing same behavior for not to go to school.this all activity is going from last 22 to 25 days.we had done the medical checkup related to stomach pain n vomiting,all checkups and tests are normal.please suggest us what we have to do regarding this issue...