Dhobi's itch is a common term for "tinea," a fungal infection also referred to as ringworm, which can be called athlete's foot when it infects the feet and jock itch when it infects the groin. It is a very common infection that tends to grow well in moist areas and is very contagious. It can be spread by skin-to-skin contact with infected individuals, or by sharing clothing or showering / washing water or areas.
The symptoms of ringworm infection are very characteristic, and include a characteristic rash that is red with "central clearing" - a red ring around a normal-colored area of skin. It is often circular or semi-circular in appearance, as the rash starts as a small red patch and grows outwards from there in a circular pattern. It is typically very itchy, and can have associated skin flaking / crusting when it is bad enough.
Your complaints of itchiness and rash around your groin could be jock itch, but there are a large number of other problems which can cause a rash and itchiness in the groin. Only a trained doctor
can diagnose jock itch, as it is impossible to diagnose without an in-person consultation. You should make an appointment to discuss this problem with your doctor, who can establish the diagnosis and start you on appropriate treatment.