Six months have passed since paper has been accepted and it was not yet published - has the editor changed his mind? About 10 months ago, I submitted one little article to a journal and six months ago I received the acceptance. I uploaded the latex file and since then I didn't hear anything about it being published.

Today it appeared a new issue of the journal so I must wait at least another 3 months.

This will be my first published article and I started to become a little nervous about it.

Can you tell me if something happened, like editor's changing his mind or delaying because they consider it less valuable than other submissions?

Should I contact my editor about this?
It is very unlikely that the article has been "unaccepted", and as far as I know, most journals publish articles basically in order (modulo some special issues and things like that).

However most journals have backlogs, and can take a long time from submission of the final copy to getting the article to print.  I don't know how common that is in your field, but for math, in 2015, the AMS published some data on how long it takes math journals to publish an article; a quick glance shows that gaps of much longer than six months between acceptance and publication are common.