I need help and advice

I have taken 4 test since 14 and they positive and I went to the pregnancy center and was positive and then Sat started cramping and then bleeding heavy with dark and I went to the er Sunday and they told me I have threatened miscarriage and that the urine test was negative and my hcg level is 6 i don't know what that is and today Sep 21 went token another test and it is neg can i not be pregnant anymore is that possible in just days I lost the baby at 4 weeks I'm not bleeding or cramping anymore..as anyone gone there this