Almost anything is considered normal when it comes to your periods while breastfeeding. All women experience a time of postpartum bleeding following birth which is not considered a menstrual period. If bottle-feeding, most mothers will have their first real period not long after this. Breastfeeding, however, suppresses menstruation at least for a while. For some mothers, there may be an absence of menstruation for weeks, months, and even years while still breastfeeding. Some mothers will even need to completely wean before they see their first period. Others, once their babies begin taking supplemental foods or sleeping longer periods at night, will see the first period. Once menstruation returns it may continue to be irregular during lactation. It's not uncommon to have a shorter or longer than normal period while breastfeeding. It's also not abnormal to skip a period or see the first period return and then find that months pass before the next one.
Perhaps you should use another form of bc such as an IUD to keep your mind at ease.