<?php $orig_post = $post;
global $post;
$categories = get_the_category($post->ID);
if ($categories) {
$category_ids = array();
foreach($categories as $individual_category) $category_ids[] = $individual_category->term_id;

$args=array(
'category__in' => $category_ids,
'post__not_in' => array($post->ID),
'posts_per_page'=> 4,
'ignore_sticky_posts'=>1
);

$my_query = new wp_query( $args );
if( $my_query->have_posts() ) {
echo '<div id="related_posts"><h2 class="headrelated">Ostatnie wiadomości w tej samej kategorii</h2>';
while( $my_query->have_posts() ) {
$my_query->the_post();?>

                    <article class="col-md-3 col-sm-6 grid3 relapooscla">
                        <div class="featured-thumb relaposclao">
                            <?php if (has_post_thumbnail()) : ?>
                                <a href="<?php the_permalink() ?>" title="<?php the_title() ?>"><?php the_post_thumbnail('grid3'); ?></a>
                            <?php else: ?>
                                <a href="<?php the_permalink() ?>" title="<?php the_title() ?>"><img src="<?php echo get_template_directory_uri()."/assets/images/placeholder2.jpg"; ?>"></a>
                            <?php endif; ?>
                        </div>
                    <div class="out-thumb relaposclat">
                        <header class="entry-header">
                            <h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php the_title() ?>" rel="bookmark"><?php the_title(); ?></a></h2>
                        </header>
                    </div>
                    </article>
<?
}
echo '</div>';
}
}
$post = $orig_post;
wp_reset_query(); ?>