Possible Pregnancy

We’ve been trying to conceive for a number of months now. On December 22 I did a pregnancy test and could see a very very faint line, I was 2 days away from my period. I decided to leave it a few days and retest again if my period was late. Later that afternoon my period started so I assumed that I hadn’t seen the line, and my mind was playing tricks on me.

Fast forward to today, December 30, I’ve had some pregnancy symptoms the last few days which I had with my first so decided to take another test, this time it was a clear, dark line.. very obviously positive and came up immediately.

The bleeding I thought was my period lasted 4 days, and soaked tampons and pads.

What could have happened? Chemical pregnancy, if so I’ll test again in 7 days and then I assume that will show negative?

Was it heavy implantation bleeding, does that happen?

Any thoughts?