What Murmatron 2 means is that in this part of your code: <?php query_posts('cat=13,14,15,16,17,18,22&showposts=5'); ?>
you should remove the part that says showposts=5. You are telling WP that you only want to show 5 posts. I had this problem recently and had to remove it from the index page. You can go to wp-admin/options-reading.php to change “Blog pages show at most” to 5. That worked for me.