What is wrong if my TSH is just too high?

My thyroid gland has been removed completely, and I'm on T4 medication, but my latest blood tests revealed my TSH rose to 38.000, the normal apparently being 0.1-0.3, and it remained the same for two more blood tests (my doctor's face of utter bewilderment was absolutely hilarious).. just for curiosity, anyone has any idea what's going on here? Thank you very much