When we first got Maci she was the same way. She would poop 7-8 times a day and it wasn't always normal consistancy I was worried about her too, but the vet said that all dogs are different so as long as she was otherwise healthy we'd just watch her for a while since she was still a pup. She stopped that after a month or two though. He also suggested changing the food but you've already tried that. I think taking her to the vet is the best bet. Let us know what you find out.

Jessica