Ruth, I know you are with SIVF, generally they won't allow you to do a FET straight after the stim cycle, you need to wait for 1 month in between. You can do FET back to back. But worth to ask FS if you can.

Regarding implantation timing, trigger time in a stim cycle is considered O time, if your have 5-day blastie transferred, than the implantation time should be about 1 to 4 day after your transfer date based on you theory. I hope that makes sense...

Try to relax and stay positive hun, the time I got pregnant, I absolutely felt nothing, it was only like 3 days before b/t, I had this sudden feeling in my lower tummy like embie trying to snuggle deeper and it only last about 3 seconds. That was about 10 days after ET.