Yes, it's perfectly normal. Each woman's body is different. Some women may not have a period the whole time they breastfeed but many start the month after the birth. If you think something's wrong, tell your doctor.
While many breastfeeding mothers do not get their periods while breastfeeding this is not always the case and is normal for periods to return soon after giving birth.
Absolutely. If it becomes highly irregular, talk to your doctor. But it's probably fine. There is a log happening to your body right now, it's trying to adjust to normalcy.
