My pet Has had had Soft stool for a while now what should I do?

My dog is a 4 1/2 month old Rottweiler she has had soft stool (looks like a consistency of soft served ice cream that goes in a cone, The swirly ice cream) I told the vet and he ran some basic tests he said and the puppy seems to be very health and to try and change her food i changed her food gradually like I was suppose to and now she has diarrhea, I gave her cooked white rice for a whole day now and there has still been no relief for her. What should I do. The vet told after the check up that it is not a big deal as long as the stool has some form and is not runny, Is this true??