There are two places to check to make sure data sync is on. First pull down notification shade, look at your quick toggles along the top and make sure "Sync" is turned on, it will be green when on. You may have to swipe the toggles to the left to see the sync toggle switch. Second place to look is in settings, select accounts, select your Google account, select the top option where it list your Gmail address under accounts, make sure the options you want are selected with a green check mark, most importantly "sync Gmail" From your description it sounds more like the main toggle for "sync" is turned off. Hope this helps