I understand your concern.
Have a Heart to Heart talk with your son, tell him that
• You love him
• You are there to understand his feelings, needs and stresses in his life
• Care for him to have good health,
• You want to have good Mother-Son Relationship
Then encourage him to express his feelings about family members, school, teachers and the Exam; and suggest to him to have Parent-Child meeting with school Counselor to improve his studies and grades.