All the dates I had scheduled in my iPhone for 2016 are gone. Also all the dates (like birth dates) that I had scheduled to recur are gone too. How can I get these back?
Welcome to iMore! Try going to Settings >iCloud > Toggle on Calendars. If it's already on, toggle it off, choose "Delete from my iPhone", then toggle it back on. You can try the same for email. If you have a Google calendar, go to Settings >Mail, Contacts and Calendar > Gmail > Toggle on Calendars.
I'm going to assume you're using the native Calendar app. If so, start the native Calendar app on your iPhone and then tap on "Calendars" at the bottom of the screen. After that, tap on "Show All Calendars" at the top of the screen.