When Doe Periods Return After Childbirth?

Hi I am 7 weeks postpartum after having twins, I am not breastfeeding at all and my physician said everything appeared normal at my 6 week visit. However, my period has not returned, even though it appeared I might have ovulated at 4 weeks postpartum. When should I have my period back? Do women take provera to induce a period if it seems their system isn't doing what it should?