Breastfeeding didn't effect me at all but I was having trouble breastfeeding so I also bottle fed.
Well with my first baby I had the normal bleeding after delivery...which lasts a while. Then I was on the birth control shot so I didn't get a period for 3 months because of it but I'm pretty sure when I quit the shot and got the pills instead I started the very next month. Could've been the pills though.
Some women who are exclusively breastfeeding don't go back to a regular cycle for six months or more after childbirth, and some start up again as early as 4-6 weeks postpartum. Every woman's hormones will react differently after each birth.
I personally didn't have a period for over two years after my son was born. - I had the Mirena IUD placed at my six-week postpartum appointment. But when I was examined by my midwife at that time she told me that my hormones were returning to normal very quickly and that if it weren't for the IUD I would have started probably within the month - I was exclusively breastfeeding at that time.
Also remember that even if periods haven't started up that doesn't mean you aren't fertile. It is very very possible to get pregnant before your first period after birth even while nursing.
TL;DR - Breastfeeding is not birth control!