Display Published Posts Count for Certain Time Period

You can fetch the record using bellow query

$posts= get_posts(array(
            'numberposts' => -1,
            'post_status' => 'publish',
            'orderby' => 'date',
            'order'   => 'DESC',
            'date_query'    => array(
                'column'  => 'post_date',
                'after'   => '-7 days'  // -7 Means last 7 days 
            )
        ));
echo count($posts);

If you want to get last 6 month the use -6 Months