Sacs measuring a week behind?

I went for a 6 week scan today due to miscarriage history. There were 2 sacs measuring 5w1d and 5 weeks exactly. Both were empty - no yolk sac or baby. I am fairly confident of my dates as I was <a href="https://play.google.com/store/apps/details?id=com.glow.android">tracking ovulation</a> but I did conceive In my first cycle post miscarriage.

Anyone have experience with this? Is this pregnancy hopeless too? Why would my measurements be a week off?