Analytics - Pageview decreasing

Hello,

My site is working normally but the pageview suddently decrease from August.2015. You can see at this screenshot http://screencast.com/t/46tMPZ2qn

The site still have several new posts everyday and I didn’t change anything regarding SEO. I tried to optimize everything once again since i did it before by using GooglePageSpeed insight.

Not sure what’s happening? I tried to find out but no luck.

Please give me some suggestions in this case? You can use grant access for closer look if necessary.

Thank you,
Tuan