What Causes Brown Spotting With No Regular Menstrual Period?

I am a 29 year old woman 14 days late on my period. I have had two miscarriages in the past, so I know the signs of early preganancy and I am not feeling any of them. Two days ago I noticed brown spotting. I am not sure what this means. My diet, and lifestyle has not changed much from last month. I have no crampy or discomfort.