Yesterday I had some slight bleeding. It was more like spotting but only happened once throughout the entire day. My period is supposed to start this weekend so i figured i started early but nothing else happened after the spotting. Ive had irregular periods since i started my period when i was 14(now 25) so im used to not always getting a period or it being late or early. But i have never had spotting. When i bleed its a period. What would cause that?