Bleeding at 13 weeks

Camille
I started bleeding this morning and went to my doctor for an ultra sound. Baby is fine and they said it wasn't coming from the uterus. I'm still bleeding off and on and am wondering if anyone else has experienced this? Or if you ever found out where the blood was coming from? It's bright red not like a period. My doctor didn't want to insert anything inside and cause more bleeding so I feel like I didn't get a clear answer on what is happening. Thanks for your insight!