Welcome to HealthCare Magic.
I can understand you concern. If you son started watery stool after using the medicine so
cetirizine has the side effect of diarrhea. you don't need to worry. The Medicine he prescribed is for Allergy , fever.
As he is having
tonsillitis ,adenoid , fever and now with
loose motion. you should add antibiotics and bring bit changes in has Medicine.
Probiotics
syp Cefixime ( Antibiotics )
ORS ( Oral hydration salts)
syp Zinc
paracetamol.
You should watch for has hydration level , don't let him get DE-hydrated by randomly giving him ORS after every loose motion and do not forget to RE-VISIT your
pediatrician for re-examining your son.
I hope have answered your Query. Feel free to ask
wish your son good health.
Regards