cycles

Had my little one in June 02 I breastfeed up until about August I received my first period sept 27 it was. A 7 day period I am not on any bc at the moment me and hubby had sex sept 15 and the condom ripped we also had sex sept 21 and 25 of sept I was due for my period yesterday if my cycles are 28 days my ob did a blood hcg quant test and was negative what's up with my period then are my cycles messed up or does it take a while to get back to normal I really wanna go get my bc but I feel weird getting one without a period I feel as if it won't work properly I know it will but still feels weird