Could someone please help me?

I was due for my period on 01/13/2022. I had sore boobs, cramping and low back pain leading up to the 13 th which I assumed were pms symptoms. I got what I thought was my period on the 13 th. The color could best be described as bright red. However it did not fill my pad and I only showed when I wiped. I usually have a heavy flow on the next day but when I started spotting brown, I decided to take a pregnancy test which was positive.

I had a miscarriage last year which started with bright red bleeding, so I’m pretty weary. Can anyone advise me on whether implantation bleeding can happen the day of an expected period of if this is a chemical or threatened miscarriage. I called my doctors office and they will not see me until mid next week.