Possible start to a miscarriage?

I’m about six weeks pregnant, I had a positive ovulation on 3/29 my last period was 3/14.

Now my numbers doubled from 4/22-4/25 went from 538-1,309.

I started having this brown bleeding type today with not really any cramps. Could it be a late implantation bleeding since I’ve read it can stay in your body and come out later. Could I not be as far as I think i am? Or is it a start to a miscarriage 😔 it’s slowed down a lot since this morning.