I'm just wondering if she could be starting her first season & is suffering from PMT?
My first bitch used to get quite hormonal when her seasons were due, although she was never regular, so I got her spayed.
Do you have any Rescue Remedy in the house? If you do, I suggest you put a few drops in her water bowl. Normally, I get dogs to lick it off my fingers, but since she's likely to take your fingers with it, I suggest you put it in her water.
I agree with the others that you should see your vet asap to try to get to the bottom of this.