My Boyfriend And I Had Unprotected Sex For Two Weeks

My boyfriend and I had unprotected sex for two weeks using withdrawal. He would pull out and masturbate to finish. My period came two days late (but that is pretty normal for me). I am worried because my period was lighter than usual. Usually I have a heavy flow for the first two days, normal flow for the third, and it becomes dusty brown for the last two days (total five days). This month, however, it was heavy for the the first day, normal on the second, before turning into dusty brown for the last three/four days. I doubt it is implantation bleeding because there was enough blood on the first two days to fill tampon/pads. Now that my period is over, my breasts still feel enlarged, which is not normal for me. Am I pregnant? Or is it stress? I have been under a lot of stress lately (work issues, worry over pregnancy)