ER visit yesterday due to bleeding

I started getting really bad cramps on Friday but no bleeding until yesterday afternoon.  ER did bloodwork and ultrasound.  They saw nothing on ultrasound and hcg level was at 70.  Dr told me that cervix was still closed and I could be really early and that is why level was so low.  Have another appointment tomorrow to confirm it was not ectopic pregnancy since my left side has been hurting.  Has anyone had a similar situation? What did your doctor tell you?  I was so miserable at ER, all I wanted to do was leave and I asked no questions. Bleeding continues, so even though I was told it was threatened miscarriage, I know I lost the baby. I feel numb, I just don't understand how you can go from being pregnant one minute and nothing the next.