[cliceperperIa]

assalaamu 'alaykum bro Soulful

From our understanding, this "waswas" (insinuation thought) from Shaytan usually start initially with small things.

eg, after having properly washed the hands, comes the thought that maybe not clean enough. Hence, wash again once. And is satisfied.
the next time (or after sometime) when one does not make effort to combat that thought, shaytan will again whisper. And before long, it becomes a disease/illness.
Washing once, not enough. Twice also not enough. Thrice etc... will continue.

IMHO best would be for one with this problem, is to consult an 'aalim (who he/she trust), seek counselling and learn the rightful way of making "tahara".
Learn the proper way of making 'tahara' and learn the way how shaytan whispers these insinuation thought (waswas), and one have to put effort to combat/fight that thought

However, at times maybe if the illness is too severe, one may need to seek treatment from an amil/muallij. Might need to be ruqyah upon and drink water that has been ruqyah.

wallaahu a'lam.