How long does implantation bleeding last? (Assuming it happens)

So I got my period (I assume) May 22 and it's already light/spotting. When it arrived it felt like a regular period but I don't know if it could be implantation bleeding. I'm not sure how implantation bleeding would look like either (HELP). Sometimes I have regular periods and sometimes they're irregular (at times it tends to come a few days early I believe). Usually the 2nd and 3rd days are when it's heavy/medium and the rest it's just spotting/light. I'm not sure if I'm just over thinking it. I also haven't had sex since April 25 (with protection) and 2 days after that I got my period (May 27 and it was normal). I'm assuming this is my period too since I haven't had symptoms for pregnancy; nothing out of the ordinary for me.