AF due BUT spotting ONLY. Help

I have an exact cycle. Always have had one. Tried to conceive this month and had BFNs. This morning when I woke up I found a couple drops of blood. Figured that was the start of AF since it was due today. It's been hours and I have not even a single drop of blood. Usually by now I have a normal menstrual flow. I am starting to get worried. Has this happened to anyone before?