What can I do to stop recurring cystitis infections?

I have recurrent cystitis and it makes it difficult to have a steady sex life with my boyfriend, who I live with. At least once a month, I have a seriously painful few days. 

I then feel quite awkward and unsexy when it eventually passes. What would you suggest? Are there ways of avoiding it in the first place?

Cystitis may not be sexy, but it is very common. It affects about half of all women at least once, and a quarter are plagued by recurrent bouts. It is caused by bacteria from the bowel getting into the bladder via the urethra.