You don't say how large the ball is and you do not say exactly where it's located. I am wondering if it is a Bartholin
which can be quite painful. If when you hold up the mirror the labia majora
is running diagonally across the 'ball' then it is most likely a Bartholin duct cyst that is infected. Hot soaks and antibiotics may relieve it. Though most likely that it will need to be drained. You need to get to the clinic and have this looked at and taken care of. If it is not Bartholin cyst that is infected (and it is much smaller-- around the size of a pimple- an individual water filled blister- it's possible it represents a herpes
infection. If you've ever had a sore on the lip of your mouth it is possible to auto infect yourself . Again I strongly recommend you get to the clinic. There are medications which will help promote healing and prevent recurrence.
I am guessing. Please be responsible and have this taken care of. I hope you feel better soon. I'm sorry it is so frightening for you.