sounds like a fungal infection
of the groin region.
hydrocort might look as if it is helping initially, because it will suppress the symptoms, but the fungal infection will actually get worse in the meantime.
try using the antifungal cream that you have used on the foot. something with clotrimazole
would be perfect. use it twice daily for 2 weeks. if the itching is really severe, use the AF cream in combination with hydrocort.
Once this has settled down, use a powder with 1% clotrimazole as a preventive measure for the next few weeks. especially if you are in humid weather or perspire a lot.