My doctor rang and said my thyoid levels are weird and asked me for a new test?

i didnt react when it happened but now i am starting to wonder. i have been diagnosed for hypothyroidism for 4 years now. today my doctor rang. apparently my tsh 3 is okay at 1,2 but my tsh 4 is about 20 (if i remember correctly) and my doctor sounded worried and asked me to go in there to take another test next week, he wasnt even angry when i told him i had taken a bit higher dose because i felt a bit tired. Does anyone know what a normal tsh 3 level and a low tsh 4 level indicates?