It can take quite a while. It is longer if your nursing. I have 4 children and nursed the last 3. With the first, I had a period two months later. With the 2nd and 3rd, it was 6 months, and with the 4th, it was 15 months. I wowldn't worry about it. Enjoy not having it!
It is truly different for everyone, some women come home from the hospital bleeding & this continues right into a period, others go months without it starting back up, usually it is irregular and will take some time to get back to what it was pre-pregnancy. Just remember you CAN get pregnant after having a baby even if you haven't had a period yet!