What can this be?

Nicole
So I'm currently 12 weeks 6 days. Had two scans the last one being only 4 days ago. Everything was fine. Baby had a good heartbeat and was growing really well. I've had no cramping and apart from feeling exhausted I've been fine. This morning I went to the bathroom to find I was having this huge bleed, I left work and headed straight to a and e I had soaked a pad in less than 40 minutes. I've never seen bleeding like it. No clots just watered down blood. They assessed me and have no clue what it could be and have booked me a scan for Sunday and sent me home on bed rest. The bleeding has now tailed off and is barely present when I go to the bathroom. Still no cramping or discomfort but I'm such a wreck panicking if I'm going to have my third miscarriage. Can anyone please offer me there experience of its anything similar or just offer advice to get me through these next two days before the scan. 
Thank you.