One day period..?

Hey ladies, I thought I had started my period 5 days ago. But it only lasted one day, with minor cramps, days after it had stopped I was still cramping like AF was coming. I’ve read everywhere that implantation bleeding is not bright red, and mine was bright red, and enough to fill a pad, but only for one day. I haven’t had any spotting, or anything since then and my CM is thick. I am not ttc and honestly am not good at keeping track of my periods. (Which is why I re-downloaded this app) Just wondering if anyone else had the same experience and what was the problem for you. Thanks in advance.