I've had a very bad case of thrush and my toungue was not white, but there were tiny white bumps all down the back of my throat & mouth. VERY unpleasant. The white toungue from fasting was nothing like that. Plus many have said that around day 21 the toungue turns pink again... so if it was thrush I don't think it would clear up... or maybe it would from die off? But why the sudden change? I Don't know, but IMO, I don't think it's thrush. Thrush HURTS.