Bleeding, anyone else?

My Dr put me on bed rest at 5 weeks because of bleeding. I gush and fill 1-5 pads very quickly then I am usually done for awhile. A few hours to days later it happens again. I can't see much of a pattern except it usually happens late afternoon/night. They are really not sure what is causing this but ultrasound shows a lot of blood in my uterus even if I am not currently bleeding. The baby looks healthy and is growing appropriately so far. Anyone that has had this before what were you diagnosed with? Did you have the same strange bleeding "spurts"?