HCG rising but can’t find the sac😩

So I need to know if anyone else has experienced this and had a positive outcome. My last cycle was 7/26 and peak ovulation was 8/10, I have a 30day cycle normally. This app is saying I’m 5w5d and Premom says 6w1d. I went in 8/29 for HCG and they went ahead and did a u/s. HCG was 143 and nothing on U/s yet. I went back today for repeats. Nothing was on u/s again so they sent for a STAT HCG and a second opinion u/s. My HCG was 1074, but nothing is doing on u/s. They can’t find a sac anywhere. I have to go back Thursday 9/8 for STAT repeats. I’m getting worried since a sac should be able to be seen. But they did both transvaginal and abdominal and there’s nothing. It’s great that HCG is rising, but why at 5-6 wks would they not be able to find the sac.