Warm moist places are a prime place for fungus to grow and thrive!
It doesn't sound like you have a full on fungus infection at this time so thats good. Try using powder on the area - something like gold bond's rather than baby powder. Keep the area as dry as possible for a few days and see if the itching doesn't go away. To keep it dry during the day, try putting a paper towel or something under your testicles to keep it away from the skin on your legs.
If this doesn't work, there are over the counter medications, creams, that are made for jock itch and you can try one of those since they are made for what your experiencing.