Sorry I've no great input- I know our bodies can do some crazy stuff at times... especially if birth control methods are changed, we are more stressed than normal etc... things like that. But if all is the same- and no clear reason, it can't hurt to ring your OB and ask? I've never had 2 periods in one month- but I've had months my period was way later than it should of been (while off BC)-- and since having my LO (and being on a new BC) I've not had a proper period. Just spotting a few times. Which, for me, is new- as I was on BC for years prior and always consistent.
I know none of that helps you- sorry. But you know your body best.