My period was 3 days late (I’m normally very regular) and the bleeding was slightly different (lighter in colour and flow) but I didn’t think anything of it at the time. Now a week later I am still experiencing cramp like pains/heaviness and nausea, could I be pregnant?

I didn’t take a test as I assumed the bleeding was my period and didn’t need to, however these pains/heavy feeling aren’t going away. I read online about implantation bleeding however I thought it was too heavy to be this. Has anyone else experienced heavy implantation bleeding and mistaken it for a period?