I've had foul smelling periods for 5 years. others notice when i'm on it, it smells like poop. possible causes?

Bacterial vaginosis?: The most common cause of increased vaginal odor is bacterial vaginosis, an overgrowth of mostly normal bacteria. BV often occurs with odor only and little or no disharge. STDs can do it but wouldn't last 5 years. It's atypical for odor to only accompany your period, though. Is there no odor at all at other times? In any case, this should be easy to diagnose and treat; see your doctor.