Thanks for writing to health care magic.
Do not worry.
Stop cod liver
oil for atleast a month.
Once you stop it it should settle soon.
To help gut recover from the overdose , I would recommend giving him ptobiotics like bifilac
twice a day.
Zinc drops at 1 ml daily for 14 days is usually prescribed in any gut illness to help bowels heal well and recover fast.
If symptoms persist for more than 5 days even after stopping the cod liver oil or if your kid becomes very dull or lethargic, consult your nearby pediatrician
Wishing him speedy recovery.