One day of heavy bleeding

I had my normal period Jan 1-5th.. then on the 19th I had one day of heavy bleeding. I was really shocked. I’m not on birth control since October. Not trying to have a baby lol but not preventing it either. Could the one day of bleeding be implantation bleeding?? I have 3 kids.. I’ve never experienced one day of random bleeding before. The hearts aren’t accurate lol I always forget to log them.