Samsung Galaxy S5 — Help! Lost photos

So on Saturday night, I was going through all of my photos before bed. All of my albums were there-downloaded, Facebook, camera, Snapchat, etc. I got a notice that my Galaxy S5 had an update. I accepted the update and went to bed and woke up to NO photos in my gallery. The only things that were there were my Picasso and Dropbox. I didn't panic because I had all of my settings set to auto sync everything. However, when I went into my Dropbox account NOTHING has been saved/synched since the beginning of December 2015. I am losing my mind trying to figure out how I can try to recover these photos and downloads from the last 7 months. I don't know where they went or why they disappeared. Furthermore, I don't know why it is that despite having things synched up, nothing has been saving. I've tried to trouble shoot online as much as I can-I can't seem to find a system that works. I reached out to Samsung and of course they offered no support. I don't know what to do but I'm really upset at having lost all of this-and I was even smart enough to have things set to back up.
Does anyone know of some tricks or things I can do to try to recover all of these?? I will be eternally grateful if someone can offer some advice to help on this. Thank you!!