This has been asked a lot already "When are the raws being released?", "Does it get released once a month?"
Sadly all topics are closed before this question has been answered.

So, I googled and quickly found out that there is a page about Young Animal (the magazine that publishes Nana to Kaoru) on wikipedia.

Here I found this information:
It is published by Hakusensha and issued on the second and fourth Friday of each month.

Sadly, I'm not sure if the magazine is having troubles, the mangaka is on break (or if he is helping with that second live action movie) or what else would make the raws come out late.

You can also click here that the volumes are still coming out in japan.