Question about Wordpress tags- drop in ranking

I have a site where I have used white-hat only methods. It is about 6 months old and for the first 4 months my rankings for certain keywords were steadily improving. Then one day a couple of months ago, my site dropped a ton for the majority of my keywords. I assumed it was temporary, but it has still been really bad for the past 2 months. I forgot that I did this, but for some reason a couple of months ago, I thought it would be a good idea to tag my post on Wordpress. I just looked and saw that those tags were being indexed by Google and in some cases a certain article I wrote was being indexed 3-4 times by Google because of my tagging.

I'm assuming that is really bad because of duplicate content. Could that alone be the reason for my significant drop in rankings? I think the timing was pretty close for when I started tagging my posts and then shortly thereafter the rankings drop happened. I've written all the content myself, I think it's really good content, and all the links are through white-hat methods. I'd be curious to hear people's thoughts on this.