The crazy world of Google

A few weeks ago the Random Pub Finder had over 600 pages indexed in Google, pretty much the whole site, then a week ago it was down to just over 200. Now its bounced back to over 300, but where are the other 300? Who knows. The site has hardly changed during that time so I don't think it's anything I've done. The more I learn about search engines, the less sense they make.