The answer is simple. You have a blog, the content on your blog’s homepage changes with each new blog post, and as it does, so will your rankings. Have you promoted the permalinks or just the homepage?
Aside from that, your blog seems to promote a single website (Amazon) with your affiliate links, so it may have been classified as a thin affiliate site, or a set of Doorway pages by Google’s Penguin web spam-fighting algorithm. You should build websites for users, not spamming search engine result pages. A real website will provide links to many different sources, not just your affiliate links, and not just link to a single affiliate channel.