It looks like it could be one of a few things. My guesses:

Acne cosmetica: Basically acne caused by makeup. It can take a few months even to show up. Link for more info

Acne mechanica: Acne caused by physical irritation of the skin like a mask strap or something constantly rubbing against the skin in that area. Link for more info

Medication-induced acne: Sometimes various medications can cause little acne-like breakouts. Link for more info

I think it's Cosmetic acne. Have you found out what it is?