I was just thinking, the fact that it only last a few days, could be due to hormonal changes, some women get acne right before or during their period, this could very well be the case for you.
Hello~Sounds like acne to me, there are some over-the-counter creams you can get to put on them, some help, some don't. If it continues and bothers you, then probably seeing a dermatologist or your GP would be beneficial, they might give you a short term of Tetracycline to help clear it up, but from what you have described, it doesn't sound that serious.