Pregnant immediately after miscarriage but spotting?

Hi ladies,

I had a miscarriage last month and my levels, confirmed by blood, went back down to 0. I found out this month that I am pregnant again, probably a little over 4 weeks now. The day that I got my 1st positive I started spotting. It was brown then red, pink, and now brown again. It is just when I wipe and nothing on my underwear. It's been 9 days of this. Of course I'm thinking chemical so I call my OB. He has me do bloodwork 48 hours apart and it tripled in that time so im so confused. Has this happened to anyone? Is there a reason? I'm hoping it's not another miscarriage but I'm prepared for anything.

Thanks so much!