What Causes Abnormal Menstrual Discharge With Tenderness In Breasts?

Hi I was due to have my period but all I got was a very light black discharge for 2 days and my breast was tender. I took a pregnancy test and it had a very faint positive line. So 2 days later I took another test and it was still a faint positive line. So now I really think im pregnant but the breast tenderness I was having has sort of started to go away. Could I still be pregnant?