Gest Sac tiny Yolk, Dates put back by 3weeks HELP

[HopefullyOnedayzz]

Hi Im new on here but need some reassurance from someone that may have been through a similar situation.
Me and my partner had been TTC for 2years we got referred to the fertility clinic but found out I was pregnant before my appointment, at 10 weeks I began having pain and found out I had lost the baby at 8weeks resulting in a DnC.
One period after the DnC I found out I was pregnant again, after being extremely anxious I was sent for a reassurance scan at 7w4d, at the scan the could only see a gest sac measuring 8mm and said I may only be 5/6weeks.
11 days later I went back for another scan this time they found a tiny yolk within the gest sac, the gest sac had also grown to 14mm dating me around 6weeks and I now have to go back next week for another scan.
Whats concerning is the growth between scans doesn't seem enough for the time as it should be around 1mm per day.
Also could I really be that far out with my dates, can a previous miscarriage mess up your ovulation cycle?
Any advice would be much appreciated as I just dont know what to think anymore!