I tested early on my 3rd FET (resulted in DD) and again with FET 4 (BFN) and FET 5(BFP)- I didn't think I was allowed with the other ones lol.

With both successful pregnancies I got a positive 6 days post transfer of day 3's. So when I got my BT results I was already prepared especially the BFN. I always had a gut feeling with both pregnancies they would be ok as I got a BFP a week before my BT's.

Good luck and I hope you have a sticky one in there...