How to treat a nappy rash due to fungal infection?

The description of your rashes seems like hives. That being said, it is safer to consult a doctor to confirm the diagnosis of hives. If it is hives, both classes of oral medications: 1) anti-histamines such as cetirizine, telecast etc and 2) a short course of low dose oral prednisolone (steroid) should be prescribed by your doctor for quick and effective recovery. Topical steroid medications will be ineffective. Calamine lotion can help with relieving itch but it does not help with controlling the underlying inflammatory response.

Thanks for the question. Pityriasis rosea is a condition that typically presents with scattered red rashes on the trunk and arms and thighs which may be scaly. The face is often spared in this condition. There is a herald patch, often a larger patch that appears before the rest of the rashes, but this is not seen in all cases of pityriasis rosea. The face is also a very unusual site to get the herald patch. So overall, it is really difficult to comment if your rash is truly pityriasis rosea without seeing your rashes.