Doesn't work on single posts

Hi there,
this plugin seems to work really well on my frontpage, but as soon as I want to have retina images(or any images for that matter) show in my single posts, nothing happens. This is a problem I have had with another retina plugin, so don’t know what can be causing it, but really running out of options and patience. Could anyone help me?

Here’s my frontpage: http://gunmad.net/indexwp.php
Here’s an example of a single post(not showing any images): http://gunmad.net/indexwp.php?p=117

https://wordpress.org/plugins/picturefillwp/