Thanks for writing to us.
First I congratulate you on arrival of new family member.
Relax,there is nothing to worry.
Initially during first 10days baby looses some weight.and after that weight gain is there.
I suggest you to:
-give EXCLUSIVE BREAST FEEDING till 6months of age.
-cows milk is to be given after 1 year of age.
-do coconut massage
-monitor his acrivity and urine output.
-get him examined regularly by pediatrician
Weighy gain can be monitored by plotting weight on weight chart,which your doctor will do regularly.
-vit D supplementation needs to be started after consulting your doctor.
In case you observe that he is lethargic or there is decrease intake of feed and decrease urine output get him evaluated.
Hope I have answered your query.
Let me know if I can help further.
Wishing your baby good health.