If you are taking contraception as a treatment to prevent an illness, ie, PND then you aren't committing a sin imo.
I should clarify though that I'm a Catholic who doesn't strictly believe in the Church's teaching about contraception (and many other sexual issues eg homosexuality) and go by my own conscious about these things.
For what it's worth, I reconcile it by looking at the wider picture and focusing on the good that comes out of women being able to control their own fertility eg educational opportunities/economic independence/prosperity for children etc etc and ability to avoid violence, subjugation and poverty.
And, coming from a large RC family where I was the last child or "last straw" as far as my mother was concerned, I think we all have a duty to do what is best for our immediate families in terms of our physical and mental wellbeing and our overall ability to cope.
And finally, when you read the Gospels, you find that Jesus didn't have an awful lot to say about sexual morality and when he did, it was in the context of welcoming (and not excluding) those who had been judged to have sinned or acted in a way which was deemed immoral by the standards of the day.
And finally, finally
because it's late and I've had a glass of
: here's a favourite quote of mine from 'The Desert Fathers: Sayings of the Early Christian Monks' (Penguin 2003)
"A hermit said, "Do not judge an adulterer if you are chaste or you will break the law of God just as much as he does. For he who said "Do not commit adultery" also said "Do not judge".
I know, strictly speaking, we are not talking about adultery here, but same principle! Whoever said you would be "desecrating the Host" was oh so wrong.