when you were pregnant, odds are you weren't tested for herpes. odds are your new partner has never been tested for herpes either.
this could be many things going on but honestly it doesn't sound like herpes. sounds more like something else going on and now that it's popped and on its way to healing, not likely you'll get accurate answers as to what it was. should it reoccur, be seen promptly.
Talk to your partner about what testing they've had done and discuss both of you going for screening for herpes and other std's.
grace
hopefully it is just irritation... but do you think that could really be it since it was only one bump??
Could be many things, so you need to get checked. It does not sound like HPV though because warts don't go away in a short amount of time like 4 days, they also don't have any puss inside them, they are just fleshy bumps.
It sounds more like herpes, but that's not a definite obviously, it could be something completely harmless like irritation.