Unknown bleeding

This is the second time I've been checked due to bleeding this pregnancy and I'm only 8 weeks. It starts as a gush and then turns to light spotting the rest of the day and then fades. My doctors are stumped 😭. Baby has a healthy heartbeat and was even moving a little on today's ultrasound, but my random, unexplained bleeding still has no cause.

Has anyone else had something similar? It's stressing me out. I never had any bleeding with my son, but my miscarriage started with bleeding and never stopped.