it might also have to do with what pill you are on. when i was on ortho tri cyclen, my periods were still 5-7 days and very heavy. one other pill was pretty much the same way but i cant even remember what pill it was, since i have been on so many.
i have been on estrostep for some time and now they are 2-3 days and very rearely have any cramps or anything.. and are very light.
my friend was on yasmin and has very bad periods, and she never had them before.
it might just take some time.. 2-3 months until you periods get lighter. otherwise it might be the pill your taking...