Hello jesskaren,
From your post it appears that you are having an issue with uploading files using Safari.
Since this is happening on multiple websites, we would start by starting up the system in what is called safe mode. This will help isolate this issue.
To start in safe mode, begin with the computer powered off. Follow the directions found here, depending on what type of Mac you have: How to use safe mode on your Mac - Apple Support
The computer will take longer to start in safe mode, and the screen may have some distorted video as it starts up. This is normal. Once you are logged in, use Safari to try and upload a file and see if it works as it should.
If everything seems to work as expected, go ahead and restart the computer normally and test again. Starting in safe mode forces the computer to run some disk checks similar to First Aid. This can resolve some issues.
Cheers.