Your call of wp_link_pages
displays navigation immediately because echo
argument is set to 1
by default, and it means to echo result. So try to add &echo=0
at the ennd of wp_link_pages
call:
add_filter ('the_content', 'pagination_after_post',1);
function pagination_after_post($content) {
if(is_single()) {
$content.= '<div class="pagination">' . wp_link_pages('before=&after=&next_or_number=next&nextpagelink=Next&previouspagelink=Previous&echo=0') . '</div>';
}
return $content;
}
Read more about wp_link_pages
parameters in codex.