Show all images from a post in correct order?

I want to view all images on a page, I have used this function under but i don’t sort the images if i enter numbers or use the sort function in gallery and i want to use the “medium” size not the full. Is it possible in some way in wordpress?

<?php
 $args = array(
    'post_type' => 'attachment',
    'numberposts' => -1,
    'post_status' => null,
    'post_parent' => $post->ID
    );

$attachments = get_posts($args);
if ($attachments) {
    foreach ($attachments as $attachment) {
        if(wp_attachment_is_image( $attachment->ID )) {
        echo '<img src="'. wp_get_attachment_url($attachment->ID) . '" alt="gallery" width="600" height="400" />';
        break;
    }
}
}
 ?>