My menstrual cycle came on I noticed light pinkish bleeding like nothing as barely there (first time this has ever happen). My cycle always last for 5 days. Well as I noticed on the 5th day (when it's suppose to be off) my cycle as became heavy as it normal is but I have no cramps as I would normally but I do have slight lower back pain as if a muslce just been over strecthed. Is this a sign of pregnancy?