Okay ready for the dumbed down medical explanation? (It's dumbed down out of laziness btw) Girls reproduction system is a 'downward flushing' system. The 'flushing' keeps everything healthy and clean. Could you imagine if all that stayed up in you? It'd be gross and it does happen. I work in an ER and the girls that come in for 'backed up systems' per say you can smell from several feet away. Nasty. Any how so part of it's that and part of it might be hormones. Everybody's different. I'm like that and I'd say most girls are...it's another weird thing you have to deal with as a girl.