PS. I had a miscarriage a lot of years ago. There is a lot of bleeding and a lot of clots/clumps. I didn't have a lot of cramping that was different than the cramping I had felt the entire pregnancy. I never had it confirmed, but I think it was tubal. I'm glad it wasn't confirmed because the hospital usually wants to remove the tube, but I miscarried on my own.
I had some spotting at week 15. I mentioned it to my doctor at my appointment 3 days later. Since it had stopped, he said not to worry unless it was accompanied by cramping, or if I was filling up a pad every hour. He found the baby's heart beat which eased my mind. But if the doctor said that the baby is fine and there is a heart beat, try not to worry about having a miscarriage.
I had spotting from weeks 6-9 at the start of this pregnancy and one day during week 10. I'm at 13 weeks now and everything is just fine !
If the heart was beating it definitely isn't a miscarriage the heart needs to stop for a miscarriage and I heard they are accompanied by a lot of painful cramping !
Best of luck to you !