@burnout426 - Well, I'm laughing and scratching my head. When I rebooted my machine today, I only had one shortcut to Opera, instead of the two I had yesterday. Grimacing, I clicked on the one shortcut, and it opened - it was the old profile, with all the extensions I use and Sync is running.
Just to check, I looked at History, and was I shocked! It's all there!! Not only the dates I had used on the new profile, but history going back to February!! So, it seems no history was actually missing at all - it just wouldn't show before.
Sooooo, I don't know what happened, but it looks like Opera fixed itself!
Thanks again for your help - you got the 'ball rolling'!