I had sex november 11 my period is due on the 18 i missed the rest of the month of november and a week of december 18 i began spotting lightly and been spotting for 3 weeks ami i pregnant?

It is possible and iwould advise seeing your doctor as if you have been spotting for 3 weeks and this is unusual for you then something is definatley going on with your body. Like I say your doctor will be able to give you a better idea of what's going on through blood tests and maybe ultrasounds