What Can Cause Lack Of Discharge In Vagina?

hi my girlfriend and i have sex once a week. after weve had sex she doesnt have much discharge. but days when i want sex she turns me down.
lately like almost everyday after she gets off work she has a lot of foul smelling discharge on panties. she doesnt shower regularly. i think she is cheating on me with someone at work. sometimes smells like condoms kinda.