I just had a scan that measured me at 6 weeks. According to my app I should be 7 plus 3. The sonographer wasn't concerned but I'm sure that something is wrong my partner and I only had sex over the 3 nights of ovulation period (I got a uti later in the month) and didn't have sex for ages afterwards so I don't see how conception could have happened so much later.
I had a miscarriage in January that started in the same circumstances and I feel like it's happening again.