From your description it appears that you are suffering from a fungal infection of the groin area. This is a common infection which is known to recur in hot an humid climate.
Next Steps
Please visit a dermatologist and get evaluated.
Health Tips
Its very tempting to treat oneself using creams and lotions available in medical stores, but these cause only superficial healing. The dermatologist may prescribe some tests and give medicines for the same. If you are sexually active you must also take care that yur partner is also treated for the same and you can prevent infecting each other by using condoms are sex