Why domain authority decreased?

Domain authority of my website was 14 and decreased to 12 and I didn't add any new backlinks to my website. Only a month ago some comment links and 5 web 2.0 blogspot from fiverr. But I was expected to increase authority. Plus I week ago added new article and traffic increased +50 a day for 2 days then again decreased to previous traffic. I'm confused because the new article is still on the first page.