A 6 year old girl, found otherwise healthy, falls ill when she takes sweets, even home-cooked kheer. It is observed by her parents since last 2 years. She gets running nose, fever of around 100-101, weakness. She responds to cetirizine for 1-2 days and steam inhalation for nasal blockage. No cough, no wheezing.

Chest is clear during these bouts. Fasting sugar, random sugar and thyroid profile are within normal limits. What may be the cause?