If you switched from iPhone to an Android phone like Samsung Galaxy S7, your WhatsApp messages don't automatically come with you when you sign in.
http://www.youtube.com/watch?v=Jk_fLbyaB5o [youtube.com]
This tutorial will show you how to transfer all the WhatsApp chats, videos, photos and audios from iPhone to Android phone. By the way, it will replace the existing WhatsApp data.