can not load my script in plugin for frontend?

when i put this code before get_header() it load the script but when put after get_header() it does not work and i should tell you that i use this in plugin that i want to use it in frontend

add_action( 'wp_enqueue_scripts', 'my_enqueue' );


function my_enqueue($hook) {
    wp_enqueue_script( 'ajax-script', plugins_url( '/my_query.js', __FILE__ ), array('jquery') );

    // in JavaScript, object properties are accessed as ajax_object.ajax_url, ajax_object.we_value
    wp_localize_script( 'ajax-script', 'ajax_object',
            array( 'ajax_url' => admin_url( 'admin-ajax.php' ), 'we_value' => 1234 ) );   
}

via Chebli Mohamed