Nystatin and antifungal meds are usually given with short term prescriptions that last a few weeks or less. Its quite difficult to get a long term prescription that will make a serious dent in the yeast.
Natural antifungals work quite well from my experience and are worth trying out in my opinion.
SF722 is the antifungal I recommend the most. Its quite powerful and look at all of the reviews online. Eventually you can work your way to a higher dose of it if you wanted. It doesn’t really cause much die-off since its a fatty acid.
Your nutritionist seems to know how to treat it somewhat. I’d consider consulting her to see whether she knows anyone else who can treat candida. Typically naturopaths can treat gut flora disorders and MD’s do not.
You also might make more headway if you state that you have a yeast overgrowth and don’t mention candida.