Yeast infection while pregnant

I went to the Dr today and she said she was going to call in a Diflucan. I’ve had that before which is normally one pill. First off she told me she didn’t see any yeast due to me only having a small amount of Discharge I explained that for the past 2 weeks it’s been in excessive amounts and it itches. I go to pick it up it’s Fluconazole with 90 tablets saying take 3x a day for 30 days. If you tell me I don’t have one why is this prescription a whole month long???