Okay my son, Joe,
Ugh on the thrush!! Oh mama, you do not have a supply problem!! I promise. Yes, you have seen a very drastic dip in supply, however, pumping 5 ounces in one session is still more than 2x the amount most women get while pumping (most get between .5-2 ounces...total for BOTH breasts).
I'm not trying to diminish your worry/concern here. But, it's really important that we distuinguish between lowER supply (producing less than you had been at a certain time) to true LOW supply where mom cannot physically produce enough milk for baby.
I've not heard that the Diflucan causes an issue with milk supply from any LC that I've ever worked with.