Since Mycoderm-C (an antifungal) has not helped and there is no visible rash, the itching is likely due to sweat-induced irritation (intertrigo) or contact dermatitis rather than a fungal infection. Stop using the powder, as it can cause dryness and friction. Keep the area clean and dry, and wear loose cotton clothing. You can apply a soothing barrier cream containing zinc oxide or calamine to protect the skin from sweat. If the itching persists, consult a dermatologist. They may prescribe a mild steroid or non-steroidal anti-inflammatory cream. Avoid self-medicating with strong steroid creams, which can damage thin groin skin.