Help please

I went to 2 doctors taking a pee test and blood test confirming I’m pregnant. By text book I’m 6 weeks. Last night I had cramping and brown discharge and brown stuff coming out in urine occasionally leading me to the hospital. I was terrified. They did a ultrasound saying I was measuring 4 weeks instead of 6. The doctor in the ER told me my HCG was 600 and she said that was low for a 4 week pregnancy. What I looked up said it wasn’t. I just want some similar stories or advice. I am terrified. We had a miscarriage in August.