Previous/Newer Posts with Categories

0 down vote favorite

I’m having some major problems getting my older/newer posts working on WordPress when only showing 1 category’s posts on a page.

It worked absolutely fine before I was defining a category, but now my client wants one category on one page, and another category on another.

The code that I’m using is pasted below. If you’d like a temporary login, I can set you up.. this has been driving me crazy for the past 2 hours!

<?php $my_query = new WP_Query($querystring . 'cat=3&posts_per_page=8');
  while ($my_query->have_posts()) : $my_query->the_post();
  $do_not_duplicate = $post->ID; ?>

<?php /* Start the Loop */ ?>

                <?php get_template_part( 'content', get_post_format() ); ?>

        <div class="post"  id="post-<?php the_ID(); ?>">
                    <h2 class="date"><?php the_time('F j, Y') ?></h2></div>

            <div class="entry-content">
                <?php the_content('Read the rest of this entry'); ?>
                <?php wp_link_pages('<p><strong>Pages:</strong> ', '</p>', 'number'); ?>

                                </div>

        <?php endwhile; ?>

Any help would be GREATLY appreciated! Thank you.