What Causes Recurrent Fungus Infection Every Time After Having Intercourse?

hi i m a 22yrs boy and my gf is 24 we are from pakistan, we did sex from last 2
year. but from last three months she got infection of fungus and a fish like
smell came from her vagina, she treated it and she got well... but after that
every time we did sex she again get infection. although we use condom every time
and i have changed my brands of condom.although am not infected from it but she
also treat her vagina every time she get infected. a fish like smell comes from
her vagina when she get infection.. every time we did sex she again get that
infection.. will u plz tell me the reason and solution of it plz