This sounds like she is in heat. This is typical cat behavior for a response to the hormonal changes the heat cycle causes and one of the reasons so many spay a female cat as they can get very vocal and annoying.
You can see videos of cats in heat on youtube
http://www.youtube.com/watch?v=-ZIm07_cj9E
and there are more listed off to the side.
If you thought she was bred previously this may be a sign that it did not take.
Hope this helps you!
If you don't think she was bred then this may be just another heat cycle.
If you think she had access to males last heat cycle then it could be she is having a problem with a pregnancy.
Another possibility if she acts like she is in pain is check to see if she has used her litter box. Bladder stones or crystals blocking her from urinating can cause a lot of pain.
So could a swallowed ribbon, string or other non food item.
If she seems very much more in pain, rather than just treading and looking to be bred, you might consider a vet check up tonight as an infection, an abdominal obstruction, a bladder blockage are all possibilities that rapid vet care would make for a better chance at recovery.
Cat Health, Behavior, Care Expert
30+ years cat owner, rescue, breeding, study of behavior & health care