frustrated with my body

My husband and I finally had our rainbow baby in October of last year, whom we love dearly, but we decided we want to expand the family and start trying again. Now, ever since having my son, I have had a period, and ovulated like clockwork (never went back on the pill)-but literally the moment we wanted to start trying, it's gone and my period is no where to be found. I have tried to be patient, but I'm a week late with negative pregnancy tests and I'm frustrated. why does this have to be so hard??