Period help!!


So I gave birth in August, 2018. I exclusively breast feed up until 2 weeks ago. Well just last month in December I had a period that lasted roughly 5-6 days. I was supposed to start my period last Tuesday 1-7-19 and have not yet. We have used protection during ovulation and use the pull out method ever time. Could this be from hormonal changes or breastfeeding, or should I worry about being pregnant again? Haven't had any symptoms also. Please help!!