New sites with dramatic rank fluctuation

I'm new to this, so I don't entirely know what to expect when a new site is created and indexed. I've built 2 or 3 niche sites and I've purchased a few niche sites all in the last 2 weeks. The sites look decent, have about 2000 words of content to start and are already indexed. I'm viewing my sites with SerpBook and notice some crazy fluctuation with them. For instance, Site A was not ranking, then the next day it was ranking 95, then a few days later 35, then back to 180, now off of the map. Most of the sites are changing daily like this. Only one has landed in a decent position. The sites have been sitting and I have not been making changes that could trigger this effect in the SERPs.

I've read this forum enough that I believe I know what it takes to rank a site. I do not expect to be ranking really well on these just yet because I have taken 0 action on them since they were created. I have not built a single link to any of the sites. My question is what are the possible reasons that my sites would be changing rank so quickly and randomly and should I be concerned?

2 weeks is too early for search engine to determine the quality of your website.There will be a hike in ranking as you are getting started.better make some backlinks to keep up that ranking