Your problem might be related to 5. The previous_posts_link only accepts one valid parameter, and that is $label, you are passing two.
Secondly, the next_posts_link does accept the second parameter $max_pages. Here you ara passing a value of 5, which overrides $wp_query->max_num_pages. So you are telling WordPress there are 5 pages, regardless of the real amount of pages.
SOLUTION:
Simply remove 5 from your links, that should solve your problem