website dropped from page 1 to page 5

Ok really confused, the other day i changed my meta keywords so i could try to rank higher for my keywords instead of just my website name. When i checked my website after changing the meta keywords on Saturday the website had gone from page 1 to page 5. Although even though i had some server errors on the Saturday after marking the error as fixed my site went back from page 5 to page 1 again. However, after checking the website today i have gone back to page 5. As my site name is trying to compete with a popular book i do expect to struggle on page 1 of Google. Although with it being my site name, in the meta description, title tag and keywords, with 5000 odd backlinks a few from wiki, plus a PR rank of 5 and Alexa rank less than 300,000 i dont expect to be down graded so rapidley or still be struggle to get page one of google.

So personally i am just wondering whether this could be a result of me changing my meta keywords or Pinging the website to much. If this is not the case could this be a result of me resieving negative SEO, which personally as i dont really have many competetors other than a book, i can not see where it would be coming from.