Is it ok to do 2, 3-day yeast infection treatments back-to-back? And how long does it take for symptoms to disappear?

Yes, but. After finishing a 3 day yeast infection treatment most women will notice that most of their symptoms of itching and cottage cheese discharge have improved a lot. It can take several more days for the yeast symptoms to be completely gone. If they are partly improved, then it's ok to take a second 3 day course. If they're only a little better then it may not be a yeast infection - get checked.