iPhoto on External hard drive has unreadable files

I Have an older macbook (the fatter white ones) and my space filled up so I purchased an external hard drive to put my iPhoto library on (a toshiba that I formatted for Mac) I wanted to make several libraries for organization and it all worked out fine. But then the trouble started when I attempted to download photos from my iPhone 5s. I downloaded them (with much trouble) to my internal hard drive (which was free of space because my photos are on the external drive) but when I tried to move the library with the photos from my phone to the HD everything went crazy. Somehow with NO PHOTOS on my internal disk it's always alerting me that it's full. The computer runs very slow. And then on the external HD the photos from my phone are gone as far as I know. Plus some of my libraries won't even open anymore because "there are unreadable files" that are in an "unrecognized format". I have no idea what happened but I would greatly appreciate the help of someone who is better with this stuff than me! I would be devastated to loose my pictures and plus a slow computer that tells me I have no space left is making me kind of fray at the edges.

PLEASE HELP

THANK YOU!