Modifying template

Hi,
I am trying to add some extra data to the AMP single page template.
My code for the regular page is:

$tags = wp_get_post_tags($post->ID);
if ($tags) {
$first_tag = $tags[0]->term_id;
$args=array(
'tag__in' => array($first_tag),
'post__not_in' => array($post->ID),
'posts_per_page'=>10,
'caller_get_posts'=>1
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
while ($my_query->have_posts()) : $my_query->the_post(); ?>
<li><a href="<?php the_permalink() ?>" title="<?php the_title_attribute(); ?>"><?php $metadesc = get_post_meta( $post->ID, 'description', true ); echo $metadesc;?><div class="date"><?php the_time('Y'); ?></div></a>
</li>
<?php
endwhile;

However, $post->ID returns empty in the AMP template. How do I adapt my code to make things work? Thanks.