Implantation bleeding?

New to this and very confused so I'm hoping you guys can help me :) according to my period calendar I was fertile the week my boyfriend was in town and we had sex almost everyday but he never finished inside me I think (TMI SORRY!) I was about a day late on my period so I started freaking out because we aren't really trying for a baby but we would welcome the arrival. My period lasted for about 6 days, but it was incredibly light, some days I didn't even need a pad and when I did there was barely anything on it. So I was wondering if this could be implantation bleeding? I've read that it usually lasts a couple of hours to max 2-3 days but I've also read otherwise lasting a week to 10 days. Most women in my family didn't know they were pregnant until their 3rd month because they had what they thought was their period. Any suggestions would help ease my mind. I took a pregnancy test the day before I started bleeding and it was negative but I want to wait a while before taking a new one. Thank you :)