You can try Gentian Violet first. It is a natural remedy. If after a few days it does not work go to your ped and they will most likely give you Nystatin.
@queendope When you apply it you will want him in only his diaper. It is a purple liquid that is topically applied inside his mouth and on his lips. It will stain any fabric and his little face(but it will wash off of his skin with soap and water). It was this medicine that got my eldest dd the nickname "Monster". Then just dress him once it dries. And use an old bib.