What Causes Cramping Pain And Bright Red Color Discharge?

Hi myself and my husband are ttc for 4 months now this month we done everything by the book we checked which days I was ovulating and had unprotected sex during these days and my fertile days . I always have a regular cycle of 28 days and my period is due on the 19th but this morning I woke up to some cramping pains and blood the blood is a lot lighter than my normal flow and is a reddish colour but my period is not due for 6 more daysv, is something wrong ?