Well said! That's exactly what I was thinking and hoping... That if my idea is not the problem, maybe a real geek with chime in and fix it. Anyway, here goes...
There has been some new additions to Google's algo announced just a few days ago. Emphasis on "Announced", who know but Matt Cutts on how long it has actually been active, right?
They (Google) have started targeting anything that "they consider" bad, misused, search terms. Two such terms are "PayDay Loans" and anything that "They Consider" to be of a Pornographic nature.
Although your site is a classy photo studio for private "Intimate" photography and not a porn site, it does have semantic terms on the site that "They May Consider" worth lowering just a little.
Below is a link from which I got this info and formed this theory. This is probably not the problem since I'm not a big-shot and no big-shots have mentioned it, or they "have" mentioned it but found out to not be the issue. But I'm having fun with the exchange and hope to learn more myself... Just like you said above.
Here's the link (I hope)
-Gary.
Oops! I meant to add this quote from the page,
Google has officially launched a new search update to target “spammy queries” such as [payday loan], pornographic and other heavily spammed queries