light bleeding no period

My period is due any day now and I've had some strange symptoms. This is my first cycle on metformin so I'm trying not to get my hopes up. Today I thought my period started and it was just light. The bleeding was pink and stopped an hour later with only a little bit on the pad. I've been cramping for a few days now. What do you guy think? I took a test about 5 days ago and BFN