Really need some advice.

I'm kind of freaking out. I've had spotting for about a week now. It comes and goes and is brown but still worried me so I went to the er. Doctor checks everything, cervix was closed and it was old blood so he wasn't worried. Took my hcg levels and sent me in for an ultrasound. After everything he comes in and tells me my hcg level was 12,000. I should be around 6 weeks and my ultrasound was measuring 5 weeks 2 days with no heartbeat. So my levels are very high but there's no heartbeat.... How? I went back not even 48 hours later and my levels went up to almost 19,000. Shouldn't that be good? Really hoping for some advice. So worried that the babies measuring behind with my high levels.