First of all, how long did you breastfeed? Many woman do not have periods until they are completely done nursing. With my first son it took three whole months for me to have a period after I weaned him. With my second son I nursed him for 15 months and again did not have a period while nursing, but I did get pregnant 2-3 weeks after I weaned him w/o every having my period. So... it is possible for you to be pregnant and maybe it is just too early to be picked up from a pregnancy test or your periods just have not resumed yet, which is completely normal.