My old photos disappeared when I updated the operating system to Yosemite?

I update my operating to Yosemite a while ago and realized that I lost old photos. All photos predating the update are missing. My photos that were stored on my Ipad are still there. All the one from my laptop are gone. I have back-ups from Time Machine and an external hard drive. The first backup on my hard drive is the one right before I did the software update. I have not backed up my laptop for fear I might overwrite my only chance to recover the photos...it had my deceased grandmother's birthday parties. Please help me!!!