Coconut oil is my best friend in this department. It contains laurie acid and caprylic acid which neutralises the alkaline environment created by the semen (an environment perfect for the bacteria to thrive). It is very gentle and a great odor killer. I use it directly after and continuously for about 3 days to eliminate the issue and to once more restore peace and prosperity to the region. Other "light acids" that are often recommended include yoghurt and vitamin C but i haven't tried those myself.
Good luck!