There are situations when, after you just installed Ubuntu and properly configured the partitions, the swap is not recognized, meaning the system doesn't "see" it, so, you can't use that swap partition (the system will not perform as good as it should).
How can we repair it?
first, install GParted
sudo apt-get install gparted
open GParted, and search your swap (it should be named linux-swap or unknown) or choose a different partitions (like, for instance, you just observe a new unused 1/2/3 GB partition)
after this operation is completed, right-click on the new
linux-swap-->Information--> and copy the text of the UUID and close GParted
sudo gedit /etc/fstab
and paste the copied text next to UUID=, then save
Finally, restart your computer.