Organize content by month? SQL statement?

Just guessing, but try this:

$args = array(
    'post_type'      => 'my_content',
    'orderby'        => 'meta_value',
    'meta_key'       => 'start_month',

    'meta_query' => array(
        array(
            'key'    => 'start_month',
        ),
    ),
);

$thisQuery = new WP_Query( $args ); 

error code: 523