<I am new to Lactnet and have a client with systemic yeast infection with
extreme nipple pain for 6 weeks now. >

Hi Bunee, this does sound like a very persistent case of breast thrush, but
I would be wary of using the label "systemic yeast". Systemic candida
infection implies that it is the blood stream and so on. I think of thrush
in the milk ducts as an extension of the nipple environment.
Other suggestions: more fluconazole or oral nystatin, what is she using
topically on the nipples?, check her diet again, check use of dummies
(pacifiers), try anti-inflammatory like ibuprofen. And keep up the support.
Offer pain break by expressing for a feed or day or whatever.
Lisa Amir
GP / IBCLC in Melbourne, Australia