LR 5: Develop history & flagging disappeared... any idea?

Hi all,

I have had a potentially traumatising  episode this evening after opening Lightroom 5.

During my previous session on August 1st, I had just finished editing several hundred photos from a wedding I had just photographed. The chosen pictures were all flagged, some of them organised into collections (with a bit more of that left to do), and I was feeling very satisfied. I am also pretty sure that Lightroom ran a back up, but cant be 100% certain of that for reasons that you'll see... Apologies for the long story, I am hoping that someone will be able to tell me where I went wrong, and any little detail might be useful...

Tonight I opened Lightroom expecting to see everything just as I left it. Since the last session I had decided that I wanted to also give the couple B&W versions of the colour photos I had previously been editing. In true rookie fashion, I selected the photos that I had placed into collections and selected "Covert to B&W" and exported them. To my horror I realised that I had just undone the colour editing and admittedly started to panic. (Eventually I realized that I could fix that problem in Develop History, but unfortunately I have bigger problems).

While going through trying to fix things, I realised that a large chunk of my photos (about 175) have absolutely NO editing/develop history whatsoever, and this also happens to be the same group that I hadn't placed the flagged photos into a collection. I know for a fact that they were edited, flagged, etc. when I last was on Lightroom, but it's as if no one ever touched them! After a closer look, the rest of the photos now have duplicates in the original folder that are also like this but no duplicates of the 175 seemingly unedited ones.

I am starting to link I am going insane. The whole point of Lightroom is that no matter what you do (mostly) you'll always have a trail of breadcrumbs to go back through, but I have nothing. And I KNOW 110% that those photos were edited and flagged for export when I left them on August 1.

I tried to restore using a back up, but there isn't one from Aug. 1, the next most recent is a few days prior - which isn't at all helpful. It seems that something went wrong while I wasn't using Lightroom whether in the previous back-up or what, I don't know. Surely if anything, when Lightroom backed up tonight, that should have retained ALL of the information from previous activity, right?

Am I completely missing something?