hcg levels and no heartbeat

Went in for my first ultra sound at 8w2d today and there was no heart beat and baby measured only 6 w2d so they drew my blood but my hcg levels are 90,000+ on Tuesday they were 60,000. I know the date of conception is correct but I'm not sure why my levels are going up if the baby stopped growing at 6 weeks. Any input? I'm devistated but the nurse said not to lose hope cause of my hcg. But I'm just 100% on when I conceived.