So scared..

Jessie
I had some light bright red bleeding yesterday about an hour after having sex with my SO with two small blood clots when I wiped and very slight cramping. Just to be on the safe side my SO and I went to the hospital. After being there for 11 and 1/2 hours the doctor woke me up at 5 something in the morning to tell me that they couldn't see anything on ultrasounds and he didn't stick around to elaborate on what he meant by that. (I had abdominal and transvaginal) but my blood work was good and he "thinks I'm beginning to have a miscarriage". My sister is a Nurse Practitioner and says they could be wrong because the ER is not really equipped for this sort of thing. I am supposed to be 6 weeks and other than some light bleeding again today which I think is from the transvaginal ultrasound and some slight cramps that go away when I lay down I feel fine. My question is, has this happened to any one and what happened.. really freaking out here...