Always tell your doctor everything you are taking, and let him or her advise you about what to do if you are pregnant or ttc.
I am 14 weeks pregnant and have continued taking my hypothyroid medication, levothyroxine. My doctor told me it's pertinant that I DO remain on it during my pregnancy and continue to have my thyroid levels checked frequently.
Best of luck to you in your FET. Mine was a 5-day FET with only one embie to implant. And, like I said, now I am 14 weeks preggo!
Happy baby thoughts!