InDesign not updating/saving

Hello everyone! II'm working on editing the text in an about 300-page document (textbook with text and graphics) in InDesign. I'd first started by creating an assignment in InDesign, then making my changes in InCopy (because everything on Adobe's website led me to believe that would be best for editing text), then saving and updating the changes to the InDesign file. This has been working fine since January. A week or two ago, the saving/updating process began taking a very long time. Within a day or two, the time to save or update content increased significantly, to the point where it frequently says the app stopped responding and I have to "force quit" InDesign. Adobe support informed me I don't need to use InCopy, but InCopy is unable to successfully update InDesign, so I planned to just make the most recent InCopy changes over again in InDesign. But attempting to make a change in InDesign causes a popup that says that this is not the most updated content, and it won't let me make changes until it's been updated. Again, this takes so long that InDesign stops responding. 

I've tried resetting the preferences, and then completely uninstalling and reinstalling InDesign. Neither has helped at all. And still, sometimes just trying to open InDesign (just the app, not a specific file) causes the app to stop responding. What else can I do???