Welcome to healthcare magic
I can think of possibilities of furuncle( boil) , or a lymph
node which has ruptured.
Do you have any sore or rash
over your genitals?
Some times a cold abscess
due to TB can present like this. It is usually painless but can become painful if seconarily infected
I would recommend you to consult a dermatologist
. You will require a course of oral anti biotics.
Hope this helped