Inplantation Bleeding Or Period?

So i posted on here a few days ago because my period was a week late, but that it is also very irregular. I had sex about a week and a half, and a condom was used and he also pulled out. I got my period about two days ago and it was heavy the first two days, when through quite a few tampons, but on the third day is seems to be light. So now of course, being the paranoid person that i am, i am now worried about the whole implantation bleeding thing? Am i correct that because of the precautions taken during sex and the heaviness of the flow in the beginning, it is highly unlikely that that is what it is? Pleaseeee Help!