So, if I'm not mistaken, there's very little chance of getting pregnant the day before your period because you are infertile, right? However, a series of strange combinations have happened which are keeping me worried, so I'd like to hear your opinions.

I have never had sexual intercourse with my girlfriend (or with any other woman, for what it's worth), however we engaged in mutual masturbation the day before her period was supposed to start. We think that my semen didn't ever get in contact with her vagina, however in the case that it might have happened, is there any possibility of pregnancy? (considering it happened to be so close to the beginning of her period)

She is usually very consistent on her cycle, but it happened that when her latest period, which should have started the day after we "played", just a few drops of blood came out, unlike the usual amount of blood that comes with menstrual cycles.

She has been under stress at her job and thinks that might be the reason for this abnormal period...does it make sense?

Any educated guesses will be appreciated...thanks in advance! :-)