Change in smell?

[maezy.livejournal.com]

i find this very odd to write, but my boyfriend tells me that he knows when i'm on my period because i smell different. he can't really explain how its different, and says that its not a bad smell. but that he can just tell, when he hugs me or we're in close contact like sitting on the couch. he says when he was in highschool he could tell with some of his female friends/girlfriends too. apparently the phenomenon is not unique to me. regardless, i'm still paranoid about this. nor do i understand why i would smell different. ideas?