When you see fast changes in the traffic of your website or the position of your pages on Google, it shows the Google doubts about the exact position of your website and you should try to fix it. The best solution for solving this problem is making some more quality backlinks for your website. But you should do it slowly not rapidly. Because if your do it fast, the position of your website will be worse than what it is now. So make some backlinks from new quality websites that your website didn't have backlinks from them yet and wait some weeks to see improvement on the position of your website in Google.
Here are some details on the Google Sandbox I posted over on WF: http://www.warriorforum.com/adsense...new-young-domains-google-sandbox-penalty.html
Though the sandbox theory is unproven .....most here with any intelligence would agree that it does exist. My advice build good quality links, be patient and work on your content while you wait
Does anyone have experience with having a site rank for a month or two and then getting "sandboxed?" How about dropping in serps after a quick addition of quality backlinks? I was a nonbeliever in the sandbox theory until recently.