Okay so, my period is 3 weeks late. On Friday Aug. 18 i was *supposed* to get it. Before this however, I was supposed to get my birth control at Planned parenthood. When i went in they told me to come in on Aug. 16th for an appointment. While here they conducted a Chlamydia test and a pregnanc test. Both came back negative. The woman told me to start my birth control that very day. I informed them that since they didnt give me my pills the week before I had taken Plan b as a precaution. They told me this would not interfere with my birth control. Flash forward to now, my period STILL has not come. I took a pregnancy test last week and that came back negative as well.. i took plan b before and my period was only a week late.. im very confused and currently not trusting the pregnancy tests I took.. what could be causing the late period??