Hi Darclar
The cyst is completely normal and as the MW said to you, is there to feed the baby until the placenta takes over. It's called the corpus luteum. Every month it develops after ovulation and if you are not pregnant then it just withers away when you AF starts. If you are pregnant it stays around to feed the baby.
As for your dates and the Drs being different by scan it could well be that your cycles were still a bit awry after your mc and that you ovulated later than expected.
I know it's so difficult not to worry and that you annalyse every tiny thing after a mc (I am doing the same!) but try and keep strong and believe in your baby :\)
Love and hugs, NN xxx
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