Thank you for visiting the Family Practice Forum.
Bacterial Vaginosis (BV) is not transmitted sexually. It really sounds like your girlfriend, based on the symptoms you are describing, may very well have BV. Bacterial Vaginosis is a vaginal infection caused by several bacteria including Gardnerella, Mycoplasma and Bacteroides. The discharge is typically grey/yellow grey and is associated with a "fishy" odor. To diagnose this, the doctor will take a swab of the vaginal secretions and look at it under a microscope.
I did actually have a case a few years back very similar to what you describe however, and when the "taste" of the semen continued to be very foul we gave the gentleman antibiotics for 10 days and the problem cleared up. The antibiotic we used in this case was Metronidizole (Flagyl). This is the antibiotic used to treat BV. You may want to let her know that it sounds like a vaginal infection that needs some antibiotics to clear up.
Again, BV is not a STD. However, she really should see the doctor to be examined/treated. While BV is not typically "serious", it may persist for many,many months if she is not treated.
I wish you well and let me know if I can be of further assistance.
Dean M. Tomasello, M.D.
Thanks