Sadly, there is no way to get detailed information about which Facebook or Twitter posts link to yours using Google Analytics. That is because neither Facebook or Twitter includes the information in the request. For most sites this information would be in the referrer URL, but neither Facebook nor Twitter includes any useful information there.
For Facebook, most clicks come the person's feed on the home page URL of Facebook. The referrer is only
Twitter uses a redirector to send users to your site. In that case the referrer is
http://t.co/wERCzOnce which is a URL that redirects to your site.