After total thyroidectomy
patient can be placed under TSH supression or thyroid replacement therapy.
TSH supression therapy involves giving higher dose of thyroxin medication so that TSH level
is very low(less than 0.5mU/L).When amount of TSH in your body is low , your thyroid gland stops growing as well as tumor
However TSH supression has unwanted effects especially on heart and bone and risk increases as your age increase. Moreove people having low risk disease do not benifit mush from TSH supression therapy.
So your doctor have shifted from supression to replacement.In this you take lower amount of thyroxin medication,as a replacement of natural thyroid hormone so that your TSH is in normal range. You need to take thyroxin because your thyroid gland was removed.
You should visit your doctor periodically and there is no need to worry about TSH level.