I'll field this one! I seem to have become the expert in the white tongue issue.
This can be caused by a number of things, but the main cause is an infection somewhere in the body. Many think the "white stuff" is bacteria or yeast. It is chemical. It comes from your saliva glands which are producing high levels of nitrates \ nitrites . I have concluded that this is a mechanism the body uses to create anti-microbial compounds to fight internal infections. Normal bacteria feed off this and enzymatically convert the chemicals.
The first thing I would have checked is the state of your teeth. There could be a periodontal infection and you may not know it is there. Next would be internal bacterial or parasitic infection. In some cases there may be candida albicans fungal infection of the intestines, but I would personally place that last in my check list.
Shroom