Hi SC,
I'm not a doctor and can't say if it's herpes or not, but the pattern of outbreaks doesn't seem like herpes. Herpes will some up and stay for at least a few days usually, but unless you're practically smoking after sex

I don't know if "ordinary" friction would necessarily trigger it and not that quickly. How often does this happen and how long does it take before it goes away?
I would wonder more about a yeast or other fungal infection, especially if it responds to antifungal cream. If you're getting it like clockwork after sexual contact of all kinds, I wonder if your gf might have a high yeast condition too, like Candida.
Do go to a doctor and get him/her to take a look at fresh symptoms that haven't been treated with the cream. Get a type-specific blood test done for HSV while you're at it. Keep us posted what you find out. Good luck!
TheOneInFour