Hi P.! I also had my son mid-August of this year (and have a 2 year & 4 month-old!).
To answer your question, breastfeeding suppresses ovulation for a few months - I believe the average time it will do this is 3-6 months if you are really breastfeeding exclusively. I'm breastfeeding exclusively and haven't had my period yet, I breastfed my older son yet had many, many problems, ended up supplementing with formula, and got my period again when he was 5 months old.
I guess the bottom line is, if you've gotten your period already, you are ovulating again and can definitely get pregnant again. The reason that many women get pregnant again while breastfeeding before they have a period is because a woman will ovulate before having her period, therefore you can get pregnant the first time you ovulate after giving birth, which would be before you have that first period. Also, menstruation tends to be irregular for a while after childbirth so it might seem like since you aren't menstruating regularly, you probably won't get pregnant but this is not true. According to my OB/GYN, approximately 90% of sexually active women who are exclusively breastfeeding will not get pregnant during the first 5 months or so. But of course, if you've had your period, you're ovulating and can get pregnant!
Whew, I feel like I'm repeating myself but I hope this helps!