Feeling Worried

I had a miscarriage last October 2018 due to blighted ovum. I had a spotting and bleeding but no cramping and undergo d&c. And now this year 2019, I am 10 weeks pregnant based on my LMP. I also had 5 positive pregnancy test. I went to an OB twice for check up and ultrasound. At 7 weeks she didn't find anything in my ultrasound and she said may be it's too early to find the sac. I came back after 2 weeks and had another abdominal ultrasound but still cannot find anything. I went to other clinic for transV but still no sac in my uterus. I don't feel any cramping or bleeding. And now i have a schedule for beta HCG to see if I am really pregnant. What should I do? Is there anything wrong? I'm nervous for my next check up..