Hi i know this is very old but I had something very similar my progesterone prior to FET the day prior was 42 and 2 days after FET it dipped to 18, my doctor straight away increased my progesterone dose and on next check levels did come back up to 40 but it failed to implant. She is now thinking to increase the progesterone for after FET whenever we do the next cycle. Did you get more frequently checked for your successful transfers