I am 17 years old and sexually active. My periods are regular, coming every 28-30 days and lasting for about 7 or 8 days. My period finished on the 19th of december and from the 27th of december till now (30th december) I have experienced very dark brown spotting in my underwear and today it has become a more light red colour. I know it is wrong, but my boyfriend and I use the withdrawal method. Could I be pregnant? Or could this be from stress or having too much sex?