Is this normal?

So my period was suppose to start on 11/29, but I was five days late and started on 12/4. Overall it was really light, but it only lasted for that day. It’s now 12/6 and I’m confused as to why I was late and then bled for one day. I took a pregnancy test the day my period was due, but it was negative. Does anyone have any thoughts on this?

While I know periods can be irregular, I’m just asking a question. My period is very regular and I have not been stressed or have changed anything in my daily routine. Thanks.