SUPER FRUSTRATED!!!!!!!!!!!!!!!

I believe the warning may be related to your storage space on iCloud. You get 5GBs at no cost. Your devices that use iCloud for photos and other data may have used up most of the 5GBs. You need more storage space - iCloud storage upgrades and downgrades. Also, see iCloud storage plans and pricing and Manage your iCloud storage.

To check storage space on your internal disk see

Get Correct Storage Information

Do not use the information from the Storage section of the About This Mac dialog. Ignore the Storage information as it is typically wrong. To find out the correct information for any disk: Select a Desktop disk icon. Press Command-I to open the Get Info window and look at the topmost panel displayed. You will find the disk information displayed for Capacity, Available, and Used. If you have more than one disk/partition then repeat for each one on your Desktop.

The categories found in the Storage section of About This Mac is simply an arbitrary way of displaying files on your drive. There are no such categories actually on the drive.

Just in case you are wanting to back up using iTunes, can you tell us how much storage your model has (or simply tell us exactly what model/year it is) and how much empty space is left on your drive? To find that, highlight your Macintosh HD icon and then hold the Command + i keys at the same time. You will get a popup window with that info - please post it here (capacity, used, and empty space).