What Causes White Discharge From Vagina?

Hi, Im a 16 year old girl, i was wondering something about my private part that maybe a gynacologist could help in. i try to stay clean & fresh down there. But for some reason there is a whiteish clearish substance that comes out of there when idk why it does & it gets on my panties & has a bad smell, idk how to stop it or prevent it because its kind of embarassing & no one knoes but please i need your help ASAP . Iv had this ever since puberty .