Part of what makes thrush so tricky is that there aren't always clear, consistent symptoms that can distinguish it from other problems. It's one of those conditions that is diagnosed by the absence of evidence that it's something else.
There's a post at bestforbabes.org (disclaimer - not an LLL source) about what other possibilities should be considered when it looks like thrush.
It's Thrush. Or Is It?
If it looks like a duck and walks like a duck, it must be a duck right? Not necessarily if that “duck” is thrush in a breastfeeding mom. Thrush (a yeast infection most commonly caused by the fungus Candida albicans) is a common diagnosis whenever a mother presents herself to a doctor with nipple or breast pain. Unfortunately, thrush is not as common as many health care providers seem to think, and many women suffer needlessly due to misdiagnosis.