Josie, look at your cart (or checkout) page with a browser and view the source code. (Make sure you’re using https when looking.) Take note of any incoming links (normally within your head tags). A quick look at your site shows that the 2 RSS feeds, the “All in One SEO Pack” plugin, and the link to your shortcut icon are all http. Try disabling the SEO plugin and your shortcut icon and see if that solves the problem.
