Thank you so much for your thoughtful suggestions; I will keep them in mind if I have future problems.
After 3 visits to the apple store with attempts by many employee to fix the problem, including a number of members of the genius bar,
one smart genius bar instructor /trainer was able to fix the problem.
There were a couple of software issues, but the biggest problem was this:
Most apple employees didn't even know it, but if you make changes in PHOTOS (downloading new pics , making albums, etc..),
then leave Photos open and try to sync with iTunes, it doesn't work; it doesn't see the new pics and changes.
You have to CLOSE PHOTOS AND CLOSE ITUNES, THEN REOPEN ITUNES and sync your phone (by usb) so it can read PHOTOS changes after the photos app has been closed.
That was the main problem; easy to fix, but it took hours of genius bar and other apple people trying; I think everyone needs to learn more about the new PHOTOS app. (Personally, I wish they'd stayed with iPhoto.) I will say, the staff was all really nice and hard-working and pleasant despite the fact it was frustrating.
Also, there were some junk/faulty files (not sure of the right word) that needed to be removed by deleting all photos from the phone (leaving them on my macbook), then reinstalling them on the phone.
Everything is working fine now. (I choose not to have my pics on the cloud and not to have some documents on the cloud for privacy reasons; I like just backing up my phone and computer together.)
