Gmail not being retrieved automatically
I had the same problem.  After reading kevinf's answer, I found the solution by checking the general Google sync settings.  Gmail was not checked!

Settings-&gt;Accounts/Google-&gt;YourEmail@gmail.com Last synced MM/DD/YYYY 12:00 PM-&gt;List of Google Sync Settings.


As a side note, the Gmail app indicated that sync was turned off.  

Gmail App-&gt;Menu/Settings-&gt;YourEmail@gmail.com-&gt;DATA USAGE/Gmail sync is OFF