I had sex on dec 20,2011 using protection, my period from the previous month was on Nov 29,2011. I recieved my period a day late on Dec 30, 2011 however it was lighter than usual and more of a brown color. It is now February 1, 2012 and my period has not come yet. There are no signs of breast tenderness like I usually have. I've been extremely stressed out, should I be worried?