Early pregnancy discharge

Hey ladies! I'm currently 3 weeks pregnant with my first. I have experienced many symptoms for 2+ weeks but I haven't had my missed period yet so I went ahead and tested anyway. With 2 positive tests (about 5 days apart) and the expected period next week, I'm having a slight brown-tinged discharge. You know, the kind that comes the week before your regular period. But it's not large amounts, it's just occasional (like spotting almost). Is this normal? I thought it was the implantation bleeding, but I honestly don't know.

I am planning on calling my doctor once I miss the period entirely, so any help/guidance is well appreciated.