Missed period

Last time I had sex was the end of march I haven’t missed a period till this cycle the last day of my period is supposed to be tomorrow and I have yet to start. What could this be since I had my son may last year my periods have come every month on time and glo has them down to a T. I need help understanding what this could be I know it’s possible to be pregnant and still have a cycle for a few months but im not ready for another baby and me and my ex are no longer together. What could this be outside of pregnancy