I had this same problem with one of mine, when she was a pup. Of course, it was on a Sunday-so I was afraid to wait-I figured she had a UTI. She did the same thing, and there was no blood, no other obvious symptoms except so much peeing. She was puppy pad trained, but just peed everywhere and couldn't help it. I took her to an emergency clinic, and it was a UTI. They gave her a script for amoxicillin-10 days worth. It only took a couple of days, and she was much better. That is probably what it is. Better call the vet in the morning! Don't wait a couple of days. Hope she is better soon.