Why does my vagina smell fishy?

Bacterial vaginosis?: The most frequent cause of strong vaginal odor is bacterial vaginosis, an overgrowth of mostly normal bacteria. BV odor typically is fishy, as you have noticed, and sometimes there is increased discharge. Trichomonas and other STDs are more common in BV, so have an STD check. This should be easy to diagnose and treat; see your doctor soon. Good luck!