Breakthrough bleeding?

Has anyone experienced breakthrough bleeding around the time that their period would be? Looking for reassurance that what’s happening is normal.

I (35F) am 8w4d into my 2nd pregnancy. I didn’t experience any issues with my first and I have a perfectly healthy almost 2 year old. I haven’t yet had a prenatal appointment, labs or ultrasound for this pregnancy and I’m not scheduled until the 29th. I had a very dark positive pregnancy test a month ago and all the accompanying symptoms.

For the past week or so, I’ve been finding dark brown spotting in my panty liners. I’m out of town with a family member in the hospital and of course that’s when shit hits the fan. Two days ago, I had a BM and passed some bright red blood and some gray-ish tissue about 2cm in size. I was straining (thanks constipation). Yesterday, I passed more bright red blood the few times I went pee. Then some dark red small clots and that’s continued through today as well. It’s been a small but constant amount with some cramping, but hasn’t progressed to heavy or period-like bleeding. My OB says he will schedule an US and labs when I’m back in town but couldn’t say whether this indicates I’m having a MC. I’m so worried.

I’m not sure if it could be a subchorionic hematoma from straining to poop, or even from stressful exercise I did the week before. Or if it could be breakthrough bleeding because I’m 8 weeks and my period would normally start now. Has anyone else experienced this?