Please help!

So,I'm having a lot of emotions right now.

1) My first scan was 7/29, where it was a surprise that I found it I was preggo at my routine yearly checkup. Took an internal U/S and showed a thickening uterus. Based on my last period, I should have been 5 weeks pregnant by then.

2) my second scan at 8/8 showed just the sac, no baby. Took blood and everything was OK.

3) my third scan was 8/21 and showed a very very very small baby with a very slight flicker for a heartbeat. Doctor was a little concerned about that, but told me to stay positive.

4) now, today, 8/26 was my 4th scan, and showed a bigger baby, measuring about 6 weeks, but still a weak heartbeat. Doctor seemed more concerned this time, and started talking about possible miscarriage. but scheduled me to come back next week

Going back Tuesday, but am really stressing out. Any helpful advice or has this happened to anyone else?

😔