How do I know if that was my period or implantation bleeding?

I started having sex when I was 16 years old. Although I never thought I would I have never used contraception before. I have had sex approximately 20 times without contraception, I have not gotten pregnant. (There has only been two guys) I have been scared of getting pregnant (especially my first time) but as a stubborn teen, I continue to refuse to use a condom and I don't exactly know how to approach my mom about birth control, I'm working on that because it's better than what I am doing now. I am now 18 years old and has had unprotected sex about 4 times in the past 3 weeks. He would pull out...but he pre cums a lot! And sometimes we went at it again right after he wiped, one time like 2 minutes later. Me and my boyfriend was so worried that I was pregnant. I had planned to take a pregnancy test 2 weeks after sex but my period came on about 8 days after. If you are a female you know how you get that feeling days in advance of your period coming on? well that's how it felt for me for about 3 days. This is where I'm a little confused: I've done some research about early pregnancy symptoms and of course it varies from women to women but I read something about Implantation Bleeding. So how do I know if that was my period or implantation bleeding? Should I wait to see if I feel any other symptoms?
Sorry it's so long...I just wanted to be clear on what I was asking! Thanks