What Causes Spotting?

Hi doc, am 22 yr old.. previously i had heavy bleeding during periods. am newly married. am xpecting periods this week.. Bt i noticed that frm 2 days i jst had traces of stains to be briefd dark brown stains.. is that a possibility of being pregnant? bt i don have any othr early signs of pregnancy like morning sickness or tenderness of breasts , aversion towards food or even nausea. could u please help me on this..