Spotting/Bleeding at 11w6d?

Hi guys, this is my first ever pregnancy and I'm 11 weeks and 6 days, last night (my birthday) I noticed some pink spotting when I wiped after the restroom, it started turning red and I got worried since I'm already high risk (type 1 diabetic) and went to the ER since it was starting to increase in amount. They did a speculum exam and ultrasound and the baby is fine and moving around but they don't know why I'm bleeding? It even picked up amount and started becoming RED right before they discharged me. Is it normal to bleed like this? They said they really don't know but it could be a blood clot behind the placenta, has anyone else experienced this or something similar and if so what happened? I had am still having mild cramping with it and just super anxious about this baby, thank you!