I am a healthy, 18 year old female. I've always been extremely regular for my periods (28 days), up until last week. I have been sexually active. But my period has been late for the past week. Yesterday I had some brown spotting and little blood. Today, no brown spotting, but I have red blood, except it's not like my "regular" period. It's much lighter. I don't have any symptoms (such as cramps, headaches or breast tenderness) that I normally have with my period. I'm not on the pill. Any idea what is going on?