Underweight issues

Okay, i know i have blogged about son's underweight issues many times before,
but it still bugged me.

I was rather upset after some comments on his weight last weekend when we were at a friend's house.
I came home and couldn't sleep that night.

I kept questioning myself,
is there anything else that i am not doing right?

I make sure he has enough food.

Balance meal, milk and supplement.

So what's wrong? Why is he still looking like a under-nourish 3 years old when he is already 5!!