What Causes Brownish Vaginal Discharge And Menstrual Cramping?

yesterday was suppose to start my period but instead i only had brown spotting not heavy or anything, but today its gotten heavier and its really dark with no blood and then it goes back to really light ive also been running a slight fever up until i was suppose to start i also had cramping yesterday along with back pain but dont have it anymore. what does this m,ean