I have a foul smell in my vagina for the first time in the history of my menstral cycle what could be causing this pungent foul smell?

Bacterial vaginosis?: The most common cause of foul vaginal odor is bacterial vaginosis, an overgrowth of mostly normal bacteria. A thin, white or gray discharge often also is present. Trichomonas, an STD, also can do it but is less common. Also foreign body, e.g. forgotten tampon. STDs don't cause odor, but gonorrhea and chlamydia are more common in women with BV or trich. See doctor for diagnosis and treatment.