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with bad odor, usually indicates Infection in Vagina. iThe most common cause is bacterial vaginosis
. Though there are many more causes for it like vaginitis, STD"s like Chlamydia,genital warts, Gonorrhea, cervical cancer
, Vaginal cancer
, Polyps etc.
I do not think that B Complex is the cause of smelly vaginal discharge, though if you have taken some Antibiotics also, it can cause Bacterial vaginosis.
I would suggest that you go to see a gynecologist, who can do vaginal examination to confirm the diagnosis, and give you proper Treatment.