HI!
There are a number of things I want to address in your situation, so please bear with me.
First, I can't see the site, so I can't verify the content on your site as 100% unique, relevant, and design with the user experience in mind. You need more than just reviews and images to have a great page, so if that isn't already the case, that is the first place to start. For any user search, ask what the best page is and beat that in terms of content. If you aren't sure how to be better than the best, find users that are looking for that via surveys and ask them.
Second, I am assuming a number of things. It sounds like your site just launched late 2013. This is based on your timeline and relatively low DA. If that is true and your timeline is accurate, you should be going through some major fluctuations. Your site is new, which means Google is actively testing it's content. Your rankings will change heavily in the first few months. You then noticed a number of onpage issues, and those were just changed as of last week. It's going to take some time for that information to be updated.
Third, based on the above and what I've seen in the past, it's very normal for your rankings to fluctuate. If you're checking by a rank checker tool, it'll fluctuate as none of them are accurate right now. If you're checking yourself, then the same IP is looking it up repeatedly, acting like a rank checker. Normal users can see ranking fluctuations per day based on the tons of factors that go into ranking.
I would highly suggest not tracking ranking, but rather watching the organic search traffic going to the page you are targeting here. That's the only way to show real success.
Fourth, tracking domain authority over time is not valid. Domain Authority change numbers based on the Moz data set. You could "lose" domain authority in one time period and still get more traffic. DA is only to be used in comparison to other sites related to you.
In the end, be patient, focus on your content and track organic traffic to important URLs to see how things are performing.