Hello,
It looks like oral thrush. Thrush appears as white patches in the
mouth. Usually they can be seen on the
tongue, inside the cheeks, on the inside of lips, under the tongue, and in the back of the throat. I suggest you to get an examination done from your doctor and get a KOH examination of the scrapings done of these white coatings.
Nystatin (Mycostatin) liquid is used by swishing a bit in your mouth several times a day and then swallowing the medicine.