My 3 week old baby has suffered nappy rash for over a week now, we have tried creams such as sudocrem, give area lots of air time and have stopped using shop brought wet wipes yet rash is still persistent?

May need a visit: Many of these are yeast and will require a anti-fungal medication. You can call the kids doc, since some will call out the prescription meds, but they may want to see it.

Hydrocortisone: Often this will settle down with 1-2 weeks of hydrocortisone cream which is a mild steroid and can be purchased from a pharmacy. If still not settling then need to see Dr as could have a fungal infection. https://www.dermnetnz.org/topics/napkin-dermatitis/