Labwork (or maybe I should say the reading of labwork) can be inaccurate especially when doctors don't know what to look for and don't even account for rt3. My hypothyroid symptoms which progressed to the point where I literally almost died and my TSH number (which was basically what the endo looked at to determine how I was /supposed/ to feel) only went up very slowly and didn't reflect the severity of my symptoms. So your doctor could tell you you're perfectly fine when you're not.