Bleeding 10 weeks 5 days

Kay

I had unexpected red bleeding tonight, followed by what looked like a clot. I went to the ER and the doctor performed an ultrasound. The baby looked perfectly healthy and had a strong heartbeat of 173. The doctor couldn’t give a reason for the bleeding and said it’s not completely uncommon in the first trimester.

Has this happened to anyone else? They gave me meds to hopefully stop it but I wish I had a definitive answer as to what’s causing it.