Thanks for the query,
You might have developed fungal infection
Another possibility is an allergic reaction
as correctly mentioned by you.
Please get a KOH mount done.
This will help in diagnosis.
Treatment can be with oral antifungals as well as with topical antifungals.
Various antifungal powders like candid are available.
These can help reduce the moisture as well as control the infection.
Please dont use any steroid
, it can worsen your condition
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you good health,