Why is iCloud only showing items that are currently on my iPhone?

A few months ago, I checked that my Iphone was automatically syncing photographs and notes with iCloud. My phone is forever running out of storage and so I typically import the photos on to iPhoto before deleting them off my device. I have just been travelling and upon looking at 'All Photos' on iPhoto, I noticed that chunks of my travel photos are no longer on iPhoto. Sometimes it is an entire week of my trip, and sometimes there are a few photographs from a given day missing, but not all of them. The photos definitely imported correctly as I have seen them on my iPhoto since. More recent photographs are all accounted for. In attempt to recover the lost photos, I logged on to my iCloud (which has significant space left on it) to discover that there are no old photographs on there at all. It merely shows the 100 photographs or so that are currently on my iphone that have been taken in the last couple of weeks. Any ideas as to what's going on? Is there a way of recovering the photos?