Ah poor baby! I would listen to the doctors - and they may not be able to be very precise as to how long, but I would expect a week to 10 days? Can you get any aloe vera down him? I would find fruit juice quite acidic on a sore throat - can he have smoothies instead?
New stuff: GERD, Recurrent cystitis/Overactive bladder
Lifelong stuff: Food allergies/intolerance, eczema, asthma