Might be an ingrown hair still... that happened to me but it didn't get that big and I cut things open like that (that's how I found out what it was) ask your doctor next time you go
It doesn't hurt at all lol its very hard to see unless I look in a mirror with my legs opened lol tmi .. hoping it goes away on its own though
if it doesn't have a head on it, then don't try to pop it. but it might be What ^^ said. try a little alcohol and run it on there with a q tip and see if it grows a head and you can pop it.
My DR told me they are Cyst. And will go away on there own. And it does believe Me.