Just posting this thread, not really for responses, but because I know I googled this obsessively in my two week wait.
I had a FET of a 5-day embryo and tested when I was told, 15 days after transfer, and not before.
I had absolutely no symptoms of any kind until two days before the test date, at which point my heart rate started to increase a bit (via Fitbit) and I also had some diarrhoea.
That was it. I was convinced it hadn't worked because there were no real symptoms. This morning: dye-stealers! BFP!
I just thought it might be helpful for people to know that it is possible to have basically no symptoms and for it to have worked. If you look at the NHS "your pregnancy" pages it does clearly say that loads of people have no symptoms before 6 weeks (and some people not even after that) but we're so focused on symptom-spotting when we're doing IVF, aren't we?