I've had thyroid problems for a few years now. I'm on Levothyroxine for replacing my thyroid. I've been taking 150mcgs for all these years and it's never changed. I'm in a job working long hours on some days to make my hours right but all of a sudden my tag levels dropped a bit further and they have had to up my dose to 175mcgs. Why has this happened? I don't understand why it has suddenly changed.