hmmm the yellow mustard colour poo is normal for BF baby. I'm not too sure how much is too much. Kirsty was doing 2 per day around Keiran's age. And I could (still do!!) hear it a mile away
With having a cold and getting a little formula, it's difficult to say what may have been the main cause - possibly both have influenced her toilet. As long as she is still feeding plenty so she doesn't get dehydrated - I'd give it another day or 2 them possibly call my doc for advice if it continues... or call if it gets worse and she isn't feeding.