Help. Opinions.

Hi so my periods are very regular. They’ve only been off a handful of times. I am currently 6 days late. I had sex (protected) with my boyfriend maybe 4-5 days after my period. We have not had sex since. (we’ve been home for winter break.) this morning I woke up with pretty rough cramps and the past couple days I had my normal pre period symptoms. So I went to the bathroom and there was blood. (yay period.) BUT my periods are generally heavy and when I went to change my tampon, it wasn’t full like I expected it to be. It seemed to be a normal color. Is this implantation bleeding or just a lighter start?