first off, show visitors that you have a great site by getting a better theme! You did not get a penalty because of affiliate content, nor have I ever heard of, however, I have heard of sites in the past getting penalty for having do follow links to affiliate programs such as amazon, remember, google does not like you giving credit to a site in exchange for receiving paid compensation, so ask yourself, are your external links nofollow? this may also include any buttons/graphics that link to affiliate sites that do not have a no follow attribute, not going to go to much into this, so I am going to assume your content is ok, if it is, then you need to check your link portfolio; maybe you have too many low quality links and/or you may have over-optimized anchor/text in your link building efforts; bad links, over optimization are common link issues that could cause your site to get a penalty, as it is not about what you are writing about, if all else fails, then hire seo consultant for an entire site autdit, they will go through your site tooth and nail, and see why you have lost your rankings. good luck.
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