15weeks brown spotting/discharge

I’ve had on and off spotting since 9 weeks. It’s been brown and light brown. I’ve been to my ob everytime and the ultrasounds have been fine. I had one again last Friday baby was great! Measuring exactly how he was supposed to. My doctor didn’t seem concerned at all. Went back Wednesday and heard heartbeat on fetal Doppler. I’m 15 weeks today started dark brown spotting in the middle of the night. Then it stopped and is back again and way heavier. Has anyone else had this? I’m worried my last pregnancy was a MMC.