Consistency of stool when feeding formula?

My 9 week old daughter started on Similac Advance 3 weeks ago. My question is that her stool is loose and I'm wondering if this is normal. It seems like it is the same consistency of when I was nursing her. When my older two were on formula their stool was thicker consistency but that was 7 years ago. I wouldn't classify it as diarrhea but it is definitely looser than applesauce consistency. She doesn't have any diaper rash. I did call and leave message for the Dr. to ask what to do on Friday but have still not received any call back and I'm getting frustrated. She is running out of the Similac advance and I wonder what I should give her. I don't want to treat her as a guinea pig. When my older two were small I gave them Enfamil Prosobee (the milk based forumla made the older projectile vomit) and they weren't loose. I did try to switch my older son to the Similac soy formula back then but it gave him diarrhea. I'm wondering it it's a Similac thing or what the heck is going on. The doctor is just a family practice MD. We have no pediatricians in my town so I'm not sure she would know either.