how heavy and long can you have implantation bleeding?

I started my period 4 days early which is not normal for me. The first day was really light and barely a period. which also never is how my periods start. then the second days were really heavy and now being the full 3rd day and technically 4th it just stopped? so it lasted 3 days when my periods can last 5 days to a week. Is that possible to have implantation bleeding like that or am I just having a weird early period? this has never happened before and I am confused.