Understanding my thyroid

[Parkerellis]

Hi I have been on thyroxine for the past 20 years since I was 15 at 250 per day. I have it monitored regularly as I have familiar high cholesterol aswell. In the past year and half I have lost 3 stones and I put it down to being a single mam of 2 and working full time. When I had my thyroid checked at Easter this year my doctor contacted me and said he was concerned and moved my medication to 225 a day. He told me my T4 level was at 21.
I have been feeling strange recently and seeing stars if I move quickly quickly at work, also not sleeping and being exhausted in the day time.They may just be symptoms of being tired as mentioned above I'm busy.
So I have had another blood test today to check my thyroid level.
I have googled for about an hour to figure out how it can go from under to over? Is this a common thing? And is it anything I have done to cause this?
If anyone can explain to me and put my mind at ease please do
Thanks :)

I am new to thyroxine (started in April). My mum has been on it for over 30 yrs. We both had Graves' disease (overactive thyroid) and both had radioactive iodine treatment to destroy the thyroid tissue so we now rely on thyroxine. Do you have primary hypothyroidism, or were you ever diagnosed with something like Graves' or Hashimoto's disease? The autoimmune things can sometimes flip you from one extreme to the other (although it's usually going from overactive to underactive as the thyroid gland burns itself out), but if you've always been underactive it sounds like a medication issue.

From what I know about thyroxine, it's pretty common to require a lower dosage as you age. This is partly because your body processes the medication at a slower rate. If you've been losing weight you will also require a lower dosage of medication (as, to an extent, weight plays a part in the number of micrograms your body needs). It may just be a combination of those two things- you don't have an overactive thyroid, per se, but may have been taking a dose of medication that is now too high for you. This happened to my mum. She has always been pretty stable with her dosage (as in she is not one of those people that needs their dose tweaked a lot), but in the the 30 years she has been on the meds, she has needed her dose reduced twice for similar reasons to those you describe.

Get your levels re-checked and see what your Dr says. Not everyone gets the textbook symptoms of overactive/underactive thyroid.. although that feeling of being wiped out at the end of the day but not being able to sleep sounds a lot like me when I was overactive. Unfortunately I lost zero weight despite my levels being in the 'toxic' range. If it's just that your dose is a little high then it's easily remedied.

Hope that helps a bit :)

Thanks so much for your reply. I am having some bloods taken tomorrow to check my B12 and iron levels. My thyroid was diagnosed as under active when I was about 15 and it makes sense what you saying.
Again thanks again :)