The case history as mentioned in your post suggests that it might be due to fungal infection
1. Keeping the area dry & avoid too much exposure to water or sweat formation.
2. Antihistamine preparations like cetirizine
to provide symptomatic relief.
3. Application of topical antifungal
cream to tackle the causative organism.
4. Topical antibiotics can also be applied to prevent secondary bacterial infections.
If symptoms still persist or aggravate further, then it will be better to consult a Dermatologist
& get a proper examination done to find out the actual cause.
So that appropriate management steps could be taken.
Also avoid wearing tight clothes...as it will cause sweating & aggravate the infections.
Wishing a good health.