I've seen authors bring up the woman being on 'the pill' a few times, and in one case I mentioned a man having had his tubes tied... (Though, fair warning, I mentioned it in the context of 'and this is why your baby brother is so much younger than you'... Have I mentioned my impregnation fetish yet?)
The pill is fairly common (irl and erotica, when the author bothers at all). Women respond differently to the hormone adjustments... It can have nasty side effects, or beneficial side effects (or both), particularly with menstruation. It can be written as a convenient device to both address pregnancy and lessen the time frame and effects of menstruation.
That's more Nemo's department with the fetish. Taking notes here: Use female contraception's into future stories. Lots of promising ideas.
I think that is rather difficult. Maybe a mental thing for a cuckquean who gets fucked by her man with a condom on before she has to watch him finishing in another girl bareback. Like "You're too inferior to get pregnant by my seed!" Or a girl who has to wear latex panties with an internal, thick vagina condom* which reduces/changes the feeling. Or the man cums in the condom and empties it on the woman's face or force her to drink the cum. * I thought about using such a piece of clothing within a story for another purpose but didn't found much about it yet. So if anyone has some links about it, I'd appreciate if you would share them. (Especially about how it feels for the woman but also how it looks like) Though it can be an element of storytelling to create tension. Maybe the cute, polite girl suddenly turns into a "Code Red bitch", shouting and slapping her new lover. It could also be a subtle hint that a woman is going to have sex when she starts taking the pill or shifts her cycle. (besides all the other reasons a woman would do that, though that could then be used to let the man think that she wants to get laid while she just don't want to menstruate during her exams)