What's wrong?!

Yesterday I got major cramps in the afternoon. An hour later I started bleeding. I rushed to the hospital, they did blood work, ultrasounds and baby is fine (Thank God) Heart beat was 164, no infection, they couldn't find a reason for the bleeding. I'm still bleeding, but its more brown than red today. I called my OB for a follow-up but she is out of the country and I have an appointment on the 6. Any guesses on what it can be ?