Hi, I've had a light flow of dark brown menstrual bleeding for two days thus far. I am getting no cramps this time even though I usually get severe ones. I started my last menstrual cycle September 6th which was completely normal. I had unprotected sex on September 4th then again on the 12th after my menstrual cycle. Could the dark bleeding have anything to do with pregnancy? I know it's "old blood" but what causes it? I just started taking this medicine called Nuvigil, could that be a factor? Basicially -- should I be worried about this? Thanks!