I have the same problem with my doctoral dissertation: three chapters are based on three articles I wrote previously, and they include some of the text and images that also constitute the articles. I did not cite the articles in the doctoral thesis or write the sentence "this chapter is based on the article ..." and later I became concerned about this. I did not do it because after having asked to my supervisor, I did not get any clear explanation about how do it properly (I was basecally the first PhD student who had published articles before writing the PhD thesis). 

I did some research and found that the editor allows articles to be reproduced in a doctoral dissertation. However, the editor asks you to quote the article in the doctoral thesis, not as a citation, but to write the sentence "this chapter is based on the article ...". At the same time, if you publish the doctoral thesis first and then the article, you must write that the article is based on the doctoral thesis. I came to this conclsuion: my problem is not plagiarism, self-plagiarism or copyright. The editor can just claim that I did not mention it correctly, that's all.