WP_Query doesn’t works inside loop

try like this:

if ($obj->have_posts()){    
    while($obj->have_posts()){
        $obj->the_post();
        $slug = get_the_tags();         
        $obj->the_title();
        echo "<br/>";
        $queryH = array("cat"=>13,"order"=>"ASC","posts_per_page"=>-1,"tag__in"=>$slug);
        $objH = new WP_Query($queryH);
        if ($objH->have_posts()){
            while($objH->have_posts()){
                $objH->the_post();
                $objH->the_title();
                echo "<br/>";
            }
        }
    }  
}