the most current studies on Amalgam (within the last 4 years) are showing:
for Amalgam fillings to be toxic one would need levels that are equivalent to every surface of 100 teeth in one mouth (we only have 32 adult teeth).
You are correct that the most dangerous/toxic time in an Amalgam restoration is when it is being removed. But minor exposure from the removal wouldn't cause any systemic issues.
your thrush is probably not due to amalgam, but more likely do to the stress of the last week-I have fibro also and stress will cause my fibro to flareup.