6 weeks 6 days pregnant. Save my baby.

Hi Doc, last week my doctor seen a flicker of the heartbeat and the fetal bone developing.. This week when I went for a scan the doctor said she could not find a heartbeat. I have gone through ivf and this was a frozen embryo transfer done on day 15 (17th February) . 2 weeks later 1st bhcg valued 419.90 and 3 days later the value was 2799.00 My 1st scan was done on 7th March and we got to know there were twins. A week later during the 2nd scan we saw only 1 baby grow.. The other one was an empty sac so the doctor said it's a vanishing twin. This week the doctor said she could not find a heartbeat and has asked to repeat the doppler scan next week. I am very tensed since we saw the heartbeats last week and this week no heartbeat. Please help! What can I do to save my baby.