Yes of course you can. Breastfeeding CAN delay ovulation but isn't a guarantee - I nursed my son for two years but got my cycle back within three months. And of course you will ovulate before having a normal period so there's no way to know whether you're fertile or not. Protection is your best bet - and since hormones are so crazy in those first few months postpartum it's best to use condoms in addition to the hormonal BC of your choosing.