Help!

My cycles usually last 29 days. I am on the pill, and have always had very regular periods, but this past week it never came. I took the pill perfectly this whole month (no missed pills), and only had sex at the beginning of the pill pack and during the last week of the pack. I took two pregnancy tests (both neg.). On the day my period was expected, I wiped a tiny thread-like streak of blood, and the same thing happened the next day then stopped altogether. I'm extremely anxious and stressed because of my missed(?) period. Any advice/similar experiences???