Hi. So my boyfriend visited 3 weeks ago and we had protected sex. I'm not on birth control but we did use a condom. 2 weeks after, my period came right on time. It was a regular period- light, then heavy, to light flow again. I'm still worried that I might be pregnant because I've heard about implantation bleeding and stuff. Should I be worried? I don't feel any changes with my body except for being nauseous one day because of something I ate. Should I be worried?

(I am of age to have sex, I am 20 years old but haven't seen my boyfriend for 2 years cos I immigrated to another country so we couldn't resist. I've always been paranoid of possible pregnancy, sigh)