I finally find the answer of the empty feeling.
Today, I've watched an interview of Oprah with J.K. Rowling. And the famous author has said it all for me.
"When you feeling sad, you can cry. But, not when you're feeling depressed. You would feel empty and hopeless."
And that's the answer, why I was feeling empty? It's because I was depressed!!
Yay! At least now I know what's happening to me XP