Dosn't sound like a parasite more bacterial, but need to check.
Any signs of flicking and rubbing.
Fish can get columnaris spots on the mouth they will look a greyish white sometimes with red tinging.
Any redness to the spot like on the outside of the spot or a red centre.
So no grain of salt any where on the fish apart from the mouth.
No grains of salt size spots on any other fish.
Whitespot does tend to start on the mouth, but you never know.
If you think its definately not whitespot you will need a bacterial med.
Can you issolate the fish for treatment.