I've had terrible cystitis regularly since my teens. I had it almost constantly throughout my pregnancy, it caused complications which led my placenta to abrupt and an emergency c-section. I'm still getting it 8 months on from the birth too.
I wear clean cotton pants and don't use strong fragranced soaps to wash down there.
Has anybody ever found a solution to preventing recurrences of cystitis when you're prone? I'm getting to the end of my tether with it, it's horrible.