7 weeks or not I'm confused

Hello ladies I'm a nervous wreck I'm not even sure how far along I am. I'm supposed to be 7 weeks 5 days but baby is measuring a week behind. Also my first ultrasound on the 9th baby heartbeat was 90 considering I was 5 weeks 6 days my doctors said it seemed fine so last Thursday baby heartbeat was 62-63 and measuring 6 weeks 4 days and my ob told me I need to cancel my prenatal care because I'm having a miscarriage and she'll be surprised if this baby makes it. Mind you 2 years ago I gave birth to my stillborn son full term so this is very sensitive to me! I have an ultrasound appointment tomorrow to see what's going on with my baby. I've had miscarriages in the past so I know what it's like and I don't have any of those symptoms no bleeding no spotting no cramping or anything. Please have anybody been through this similar situation as me? Please also keep us in your prayers 🙏