Hi,
Noted the history about your 3 year old son having 
diarrhea 10 times a day even after giving Erceflora and zinc, it is soft to watery and you have posted 
stool test which is normal hence Entamoeba is ruled out at the moment.
For this I would advise the following:
Get the stool tested for 2 more days as this needs to be done as one of the tests may show something positive.
Also get the blood tests done for CBC and electrolytes.
If there is any evidence of an intestinal infection then he may need a course of suitable antibiotics.
Metronidazole is given if there is any evidence or if his 
Pediatrician is prescribing on empirical basis.
Give 
Pedialyte electrolyte solution meant for pediatric patients.
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. T. Chandrakant, General Surgeon