Ah, I first went under active in my third pg, this is my fourth. I had myself tested regularly for years anyway as my dad is hypothyroid and all three of my sisters became under active before they were 30, so I suspected mine may play up at some point. The levels were always fine before, but I asked for them to be tested when pg with my daughter and they told me they were low but 'sub clinical'. I never knew the actual numbers throughout that pg, I didn't know quite how important it was at the time, but luckily all turned out well.
I think in a way ignorance is bliss as I've fretted often about it this pg and scared myself by googling. I had my thyroxine increased from 75mg to 100mg at 6 weeks, and a blood test a couple of weeks later showed my TSH to be 3. The doctor said the level was 'fine' but after reading online that NHS guidelines state that when pg levels are best kept below 2.5, I contacted my midwife who spoke to the endocrinologist who confirmed that is what they want. I related this to my GP who raised my thyroxine further to 125mg. Another couple of weeks later my tsh was at 0.9, and a few weeks after that was 1.3, so I'm hoping the new dosage suits me. I have it checked myself monthly anyway to keep an eye on it.
Have they ever thought about giving you thyroxine as soon as you conceive to counteract the sudden impact on your levels? Or are your pre pregnancy levels good enough to take a low dose while trying to conceive?
I have found regular GPs a bit rubbish and slow at all this. When I first asked for my dose to be raised, I saw a locum doctor who wanted to test bloods before changing dose, despite guidelines recommending an immediate increase. I was already 6 weeks, and they had no blood appointments for over a fortnight and she thought that was ok, but I wasn't happy and phoned back. That same doc phoned the endocrinologist herself to check and was told to increase immediately.
If something doesn't feel right, push for further answers. I hope they got on top of it for you xxxxxx