Dropped hcg levels

Hi can anyone please help me. I thought I was nearly 7 weeks pregnant and on Friday had bad cramps and a slight bit if fresh blood only when I wiped just once. I did have brown discharge and 3 days later still have brown discharge. I went to a n e and they took bloods and told me to go for a scan Sunday. When I arrived Sunday my bloods were 720 they did a scan and I was measuring 5 1/2 weeks there was a yolk sca which I was told was good news. When I went to see the midwife for another blood test after she changed my notes to read no yolk sac which confused me she took more blood and has rang me this morning to say my bloods have dropped to 562 and that it's not good news I'm niscarryinf but to go in tomorrow for more bloods to make sure. I'm completely confused as I was told there was a yolk sac but she changed to no yolk sac can anyone help me please