Skidders, Do you allow your partner to ejaculate inside you?
If yes, it can be bacterial vaginosis (BV). The bad bacteria inside your vagina gets out of balance with the good bacteria and reacts to his semen. It creates a very foul fishy smell.
The medical profession does not know why this happens but your chances to get it increase with every different man that you allow to ejaculate inside you. Around the third man, your chances get high to contract BV.
It is normally treated by a doctor using antibiotics. It is not an STD and it is not caused by your partner.
The other times some women can smell it is around their periods.