Brand name of the USB, or is it a generic cheap brand? That could very well be the issue. Also, did you try going into your media folder? In the first link, don't follow the steps under "Other Useful Commands" yet. Your system isn't detecting your USB/mount so I doubt that will return anything for you. If you know the name of the device, you can try to manually mount the USB drive. Let us see if automatic mounting is enabled first. Open up your terminal and write/paste the following commands;
This should bring up what you need to edit. If you are given errors, please share them. If you aren't given errors, continue. Next browse for "org.gnome.desktop.media-handling" and see if "automount" is set to true. If it isn't, set it to true. Reboot your computer and plug your USB into a port and see if anything pops up. If nothing does, continue with the following steps to manually mount. Run this command while the USB is plugged in;
This should list your device name(s) which should resemble something like "/dev/sdb1" etc etc remember the name exactly and write it down if you need to. Next we need to create a folder for the mounting, so put this into the terminal next;
Now this is where the name of the device comes in. Once you have the device name, do this command, switching out "/dev/sdb1" with the name of the device you got via "sudo fdisk -l";
sudo mkdir /media/usb
If that goes well, then use this command to mount the USB;
sudo mount /dev/sdb1 /media/usb
When you do the sudo command to list devices, please make sure you have any other USB drives, external books or the like disconnected so you will know which it is you are looking for.
sudo umount /media/usb
If none of that works, you can try Disk Utility to see if the USB is mounted and working. If none of that works, then I think it might be your brand or a faulty USB stick.