TMI: Brown thick discharge on and off 10 weeks

Hello,

I’ve had discharge like this on and off since week 6, no infection present and 8 week US showed normal pregnancy and strong heart beat. It typically comes out after bowel movement or long walk, no cramping at all. Sometimes more brown and sometimes kore tan or yellow. Doctor has said not to worry but unless it gets heavier or bright red and I have pain but can’t explain why I am getting it

but I am still worried and wonder where the old blood is coming from and why I have had it going on this long. Has anyone had this or have any advice?