No changes taking effect anywhere in backend

In trying to make any changes to anything (general settings, plugin settings, deactivating plugins, changing themes), when I click to save changes, the page reloads and all of the changes revert back.

The last time I logged in I didn’t have a problem making changes.

When I try to create a new post and save it as a draft, I’m redirected to a page with the message “You are not allowed to edit this post.”

When I attempt to activate another theme, I get the successful “Theme activated” message at the top, but nothing actually changes and the old theme remains active.

When I attempt to deactivate plugins, I get the successful “plugin deactivated” message, but it’s state does not change and the plugin remains active.

I’ve tried renaming the plugins folder. Overwrote all of the core wordpress files with a fresh install. Changed folder permissions to 755 and file permissions to 644. Nothing works.

All of my user accounts are admin, yet it *FEELS* like they don’t have admin rights.

Also, I’m not running any cache plugins

Any ideas?