Menu items won't highlight

Hello,

The problem I am having is on my first portfolio site at chrisbooth.me. The main menu at the top is a menu I defined in the admin panel that includes “Me”, “Portfolio”, “Blog,” and “Contact.” The problem is that when viewing a page deeper than the 1st page, the correct menu item won’t highlight. So for instance, when viewing the home page, “Me” is highlighted. But when viewing a portfolio piece or blog post, there isn’t anything highlighted.
When I view the source code, I see classes that appear to be the key to highlighting the correct item, like “current-menu-item” and “current-page-item.” When on a portfolio piece or blog post, those classes aren’t there.
Previously, the situation was that all pages were highlighted, but individual portfolio pieces and categories had “Blog” incorrectly highlighted, and not “Portfolio.” This changed when I activated the 2012, and then the 2013 theme, and then reactivated my theme. It is progress, but now I want to get it to highlight correctly.
I am guessing this is a PHP issue, since the “current-menu-item” isn’t being correctly applied? I have my own style sheet of course, and I use Firebug to experiment, but I can’t seem to specify a highlight via CSS. I’m worried that, even though in the Dashboard panel, there were separate sections for adding blog posts and adding portfolio items, there isn’t correct code to distinguish the posts from the portfolio pieces.

For reference I am using:
Wordpress 3.6
A child theme of a theme called Whitelight (from WooThemes)
GoDaddy.com hosting
an FTP called Transmit

I’ve looked at many different sites and forum posts, but none seem to match up enough or have solutions that work for me. (Pages like this, this, and this.) I consider myself pretty proficient in HTML and CSS, but I really know absolutely nothing about how to write PHP. It’s very embarrassing to admit. But if you know of any solution in the PHP, I would really appreciate explaining it in the simplest and most detailed way.

Thanks very much in advance, I appreciate any and all help!

(P.S. sorry this is so long I just want to be as specific as possible.)