Google ranking issues since changing theme

[PhotoActive]

Since changing my Wordpress theme from the old Lifestyle theme to the new Enterprise theme on the Genesis framework my Google ranking for specific keywords has fallen. I’ve had a look through the forum and seen someone else had a similar problem a while ago and so I was wondering if anything had changed since then.

For around 12 months my site www.photoactive.co.uk appeared in the top-half of page one for a Google search of ‘photography holidays’. However, within 24 hours of changing themes my position fell to the bottom of page three for the same search phrase.
Also, it’s not my homepage which is being ranked at all anymore but a specific page – www.photoactive.co.uk/photographyholidays.

I used to use the All in One SEO pack plugin with my old theme but used StudioPress’ SEO Data Transporter to switch over to Genesis’ built-in SEO settings, which seem great.
I’ve resubmitted my sitemap etc to Google Webmasters and done everything else I can think of but I don’t understand why the site has fallen so much and why the homepage is not ranking for my main search term at all. I must be doing something wrong but I can’t figure at what!

If anyone could offer any advice at all I’d really appreciate it!