Hi what causes excessive bleeding from my nostril and mouth just before my periods start?

Unusual bleeding ?: Bleeding from mouth/nostrils is not known to be related to the timing of one's menstruation. Get a referral to an ENT physician for an exam and testing. There is more congestion of the nasal passages immediately prior to menstruation, so with attempts at clearing one's nose, bleeding may occur, and flow back into the throat area and appear to come from the mouth.

Bleeding: Various hormonal changes happen with your period. Changes in estrogen, progesterone and prostaglandin levels can effect blood vessels and be a factor to explain your symptoms. Either way though you should be having nose bleeds with each period. I would have your nose looked at.