Does one incur sin for refusing the specialization requested by one's parents after performing the الاستخارة (Istikhara) prayer and experiencing continuous hesitation?

A child is not obligated to obey their parents in studying a major they dislike, but honoring them takes precedence. Strive to please your parents by studying medicine. If this causes you distress, try to persuade them. Choose from the sciences what suits your abilities and what the Muslim nation needs. You have done well by performing Istikhara, for whoever performs Istikhara proceeds with the matter for which they sought guidance, and goodness lies in what transpires after Istikhara.