I had this with Chloe and you have my sympathy, they changed her from nystatin to another medicine myo something? ( can't remember the name but I'm sure if you google you'll find it) They also gave me an oral treatment to clear mine up and advised I saw a breastfeeding counsellor at the clinic as poor latch can cause it too, once I did all this it cleared pretty quickly
Don't forget to thoroughly clean and dry your nipples after each feed too as any moisture will make it worse
Hope you're both better soon xx