Half of photos disappeared when converting from iPhoto to Photos app

Help!

I have a Mac Mini (Mid 2010) and I updated to OS X 10.10.3 yesterday. Today I opened the new Photos app and "migrated" my photos. Only half made it (those up to mid 2011). I then tried to open iPhoto and it had disappeared (BTW, I don't believe that it was the very latest update of iPhoto). I clicked on "Pictures" in the finder and it only had something to the effect of a "iPhoto.migratedphotolibrary" with 15.86 GB and Photos Library with 16.84 GB. My photos/video in my iPhoto before today must have been between 30-40 GB (the About My Mac storage for photos alone is 55.58 GB (movies 170.72) and I don't have a lot of extra photo/video clutter).

I went into the App store and eventually found a way to upload iPhoto again. When I did, I was able to open the "iPhoto.migrated (etc.) library" and it said that I needed to convert the files to the new iPhoto. I did. They were the same as the Photos Library (only up to 2011). I have a Time Machine (my back-up). The weird thing is that I can go back 9 months and every time, when I click pictures, the iPhoto folder has 15.73 GB. No change. We have added photos to iPhoto throughout that period (I just looked at several of this year's photos yesterday morning.

Now, the good news (I think) is that my storage numbers haven't changed. So the photos have to be in there somewhere. Can you help me get them back?

Thanks.