OK, so you’re not using AJAX (you didn’t share any Javascript here, so I may be confused as to what I’m looking at) but this line:
<?php $args = array('posts_per_page' => 1); query_posts($args);?>
indicates you are setting the number of posts to be displayed to just 1, hence the “posts_per_page” value being set to 1. To increase the number of posts display, push that number up to 10 or 20 or whatever you need.