Period question

Im on birthcontrol and i have been having unprotected sex with my boyfriend and we use the pull out method. The past few months i will get my period but it has been lighter than normal and more brownish in color the first couple of days. Could this be a sign of pregnancy? Also i have been on birth control since the summer but could it just be my body reacting to the birth control as well? Could it be stress related? I am not trying to get pregnant so i have been stressing about it these past few months. Any info would be appreciated. Thanks!