I'm young so this is a hard and embarrassing topic for me, i'm wondering why j sometimes have fishy odor "down there"?

Vaginosis: Vaginosis or other infections can lend a fishy odor to your genitalia. Please see your doctor for proper diagnosis and treatment. And don't be ashamed, biology is biology.

Vaginitis: You may be having infection in your vagina or perineal area. If it persist, talk to your personal physician for antibiotic prescription.

BV: Sometimes disturbances to the natural bacteria in your vagina (douching, irregular bleeding, unprotected sex, etc) can allow abnl bacteria like Gardnerella to overgrow and cause a fishy odor. It's not sexually transmitted, but can be treated w/ Metronidazole(Flagyl)/Clindamycin/Boric Acid. See your GYN for a prescription and be examined for other potential causes. Nothing urgent/dangerous though.