The moment my No.4 turns 16mo, my milk production stops. How did I know? Latching onto it is not sufficient to quench his thirst at night, he sucks longer and harder and when I squeeze my boobs, no more milk comes out. 
Since that day, I have to walk out of my room to prepare formula milk for him. In the beginning it is tiring but after a month, I got used to it.
After more than a month, he is still latching for comfort when he wants to sleep. I wonder when will he finally let go.
Stumble it!
Latching on is sort of a pacifier for him..