add_filter( 'the_content', 'post_navigation', 10, 2 );
function post_navigation($content) {
    $post = get_post();
    $post_type = get_post_type( $post );

    if ( $post_type == 'post' ) {
        $next_p = get_previous_posts_link();
        $content = $content . $next_p;

        return $content;
    } else {
        return $content;
    }

}

You are being timed-out out due to inactivity. Please choose to stay signed in or to logoff.</p>
<p>Otherwise, you will be logged off automatically.</p>