What Causes Cramping, Lower Back Pain, Heartburn, Fatigue And Headaches?

For the past three weeks I have been having cramps, lower back pain, heartburn, major fatigue, more frequent headaches, upset stomach, and thick white vaginal discharge. My first thought was oh maybe im just sick. But then I questioned if I could be pregnant. I am on birth control and every four weeks i get my period on a Friday night. this month i got it on Saturday night, and it was very abnormal. It started as thick discharge, like before, but brown. Only very thin colored blood is present with the clumps of dark brown stuff. Should I be worried?