And, FWIW, I too went through the "is this a latch issue?" thing...but by the time I finally determined it was thrush BOY was it horrible. I used nystatin (which I am not adamantly opposed to, because it's messy and rarely resolves thrush due to it being in a glucose base which just feeds the yeast) and when that did nothing but make it worse, I used gentian violet. I had to treat for a lot longer than normal (a week before it was resolved) because my thrush was so severe, but it worked! After that, I decided "when in doubt, treat for thrush!" I was determined to never let it get that bad again. I had another two instances, months later, where I thought it might be a latch issue. Thrush didn't seem as likely since I wasn't leaking as much, etc., but I treated for it anyway (I figured if the treatment didn't resolve it, then I'd know it was a latch issue and would proceed with that)...both times it was gone in a couple days, so it was thrush! But it never got more than mildly annoying, yay!