Implantation bleeding?

I noticed i was having brown discharge on the second thursday of my 4 week pill. I also had a very sharp pain in my uterus, my boobs have been sore and I’ve had some cramping when I usually don’t.

I did have unprotected sex the night before I started a new pack, but I took all the pills as directed and I have always been safe before.

I have experienced this before and wasn’t pregnant, but it was closer to my period…

What could this be? Could I be pregnant? Anything helps, ty!