Never happened before, please help!!

Tara

Sexually active. On the pill since I got married, almost a year ago. Periods are normal and always the same time. I started spotting three days ago and I'm freaking out because my period isn't suppose to happened until next week (according to my pills). Maybe TMI but the spotting is not my period, it's dark, thick, smells different and it extremely light! Has this happened to you before? What could be causing this!? Please let me know! Thank you!