Thank you for your query,
Your child seems to have gastroenteritis
mostly of viral cause.
Nothing to worry as he is active and eating well.
Give sips of oral rehydration solutions like pedialyte to maintain hydration.
and zinc may be added to his treatment after consulting your doctor.
Monitor hydration status by activity, urine output, skin turgor and moisture of oral cavity and tongue.
Consult your Pediatrician
for the assessment of your child and medications.
Teething is not the cause for diarrhea, but may cause loose motion
due to keeping hands into mouth due to teething irritation.
There will be some indigestion
due to rapid passage of food through the gut in gastroenteritis and nothing to worry.
Hope I have answered your query, if you have any queries in future you can consult me on Healthcare Magic.