There should be a "Docor Consultation" in the medicine store - it's pricey - $175, but it will tell you what illness (if any) your kid has. Once you know that you can remedy it. COuld just be hiccups, which is easy.

Vitamin pills do work well as others have mentioned. Also get the air purifier (in the shop) which goes in the office, it is suppoed to make a healthier environment there too.