Hi,
Welcome to health care magic,
First of all,I would like to clarify that your baby has not 
chronic diarrhea rather it is acute diarrhea (since 3 days) which might be suggestive of intestinal infection,mostly due to 
rotavirus or amebic /mixed/ bacterial infection.
Diarrhea can also be a known complication with bottle feed if the bottle is not sterilized properly before each feed.
I would like to advise you to maintain the fluid intake of the baby by supplementing with 
ORS and keep watch on the urine output.
In case If diarrhea occurs again,then kindly get your stools checked, to detect the causative organism.
Your baby will need some specific drugs (according to the causative organism) like Metranidazole,antibiotic like 
Norfloxacin, antispsmodic drugs to control the pain will cure.
Please consult a pediatric doctor for specific prescription.
Thanks and regards,