I have an 8 month old Bullmastiff. I've had her since she was 4 months. She has always had softish stools. She was on Purina One Large Breed (chicken based). I switched her about 3 weeks ago to Nature's Recipe Adult (lamb based). She now is having super loose stools, almost diarrhea. It looks pretty much like diarrhea, but she is still only going about 2x per day, so it doesn't seem like it is caused by illness. Is this caused by an allergy of some sort? How do I go about figuring out what is causing this?