WordPress loop only displays 5 articles max?

The most probable cause of this is the incorrect use of pre_get_posts, so I would look in my functions.php for any instance of pre_get_posts. I would suspect that pre_get_posts is used to set posts_per_page to 5 across the complete site.

Irrelevenat, but you make use of the build in loop counter $wp_query->current_post as a counter in stead of creating your own counter