Found out my due date is a week off

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So I’m kind of freaking out a bit. I went to the ER today at the recommendation of my doctor for severe cramping. It started out normal then got worse and worse over the past two days. They did an ultrasound in the ER. I thought I was 6 weeks but it’s looking like I’m 5. I’m keeping my fingers crossed that I simply ovulated late and it’s a viable pregnancy. I’m still in the ER waiting to hear what they think. It’s only a week off and I didn’t get my first positive test until February 18th despite testing every few days since the beginning of February. Then I got a dye stealer a few days ago. So that all seems like it adds up to me being five weeks? Good thoughts sent my way would be appreciated! I’m sure they’ll just monitor me and I won’t know for sure today.