Nystatin is an ancient, weak, dirt-cheap and side-effect plagued MOSTLY topical and toxic polyene, to which any self-respecting fungus and yeast has long ago developed immunity...
On the mostly topical and toxic part: very little of it is absorbed by the body, but what is is quite toxic to you (if your body managed to absorb it in significant amounts - such as if you injected it - would be expected to kill you). It only acts on fungi it touches, so it has to physically come in contact with the colony wherever your yeast is.
This stuff was routinely prescribed some 40-50 years ago concurrently with any Antibiotics treatment as standard procedure in many countries... even then, it was more fungistatic than fungicidal, and like the Antibiotics of those days, it has become obsolete in the fact that most stuff out there has since gotten to be absolutely immune to it.
Among pharms, the ones that actually WORK are:
fluconazole - long-term treatment, NOT the one-pill vaginal thrush "magic bullet", but weeks or months of that 1 pill once or twice daily
terbinafine - potentiates azoles through unknown mechanism, combined with itraconazole/fluconazole is able to kill yeast that neither it, nor the azoles alone can hit
natamycin - a more harmless and efficient unabsorbable polyene, think of it as modern nystatin
...voriconazole - supposedly - if you're filthy rich or got insanely good health insurance (a 100-pill pack costs ***$11 000*** in my end of the world, and appears to be for around a month of treatment, which may actually take LONGER)... effin pfizer :(
terbinafine - works better and way faster than topical azoles