Chemical pregnancy /misscariage

I don't know if anyone else experienced this before. I posted beginning of this week my exciting news that I am expecting. Took 3 positive tests and also got the positive from Dr's office with the due date being 2/20/16, and being 3 1/2 wks along. Started cramping this morning with some bleeding went to ER and they told me that I had a chemical pregnancy. They call it that way because the pregnancy was to early to be detected on the ultrasound. ER though that I wasn't pregnant in the first place, they thought that I just got my period and that I was never pregnant until I showed them my pregnancy paper from the Dr, they looked surprised and just told me it was just a chemical pregnancy and that it happens sometimes. I am soo confused because I didn't get any explanation from them. Please help