Hi,
How are you? Are there other symptoms present? At this point, try to avoid scratching to prevent secondary bacterial infection. Keep the area clean and dry and wear loose clothing. It could be due to irritation, allergic reaction or infection such as yeast infection or bacterial vaginosis.It is best that you have this checked by your gynecologist for proper evaluation. Direct clinical examination is important. Take care and do keep us posted.
It may be a yeast infection. Are you taking any antibiotics at the moment?That is a prime cause of yeast infections...they kill the normal flora on our skin and allow yeast to grow. You more than likely scratched the daylights out of it and caused the open sore. Try an over-the-counter medication for yeast infections.