I am really very sorry that you have been catapulted into ill-health due to your Endocrinologist, wrongly (he might think he's correct) has reduced your thyroid hormones.
We have all the sorry stories on this site, mainly because members are not treated optimally.
New Research (from several research bodies) have stated that most get well with a combination of T3/T4.
Endocrinologists appear to be the least knowledgeable when treating patients who have hypothyroidism but it is even worse, in my viewpoint, that they remove the vital T3 from a patient who has no thyroid gland whatsoever.
Levothyroxine is T4. T4 is an inactive hormone and should convert to T3 but many of us cannot do so efficiently or the dose of levo is too low in order to keep our results 'within a range'. Liothyronine is T3. T3 is the only active hormone required in our receptor cells and it runs our whole metabolism. The brain contains the most receptor cells then heart but it is required from head to toe.
You can source your own T3 at present as the NHS has cut back on prescribing for patients (even if the patients are unwell without it) as it has gone exhorbitanly expensive by the Pharmaceutical company - about tenfold in rise I believe.
Members have had to source their own and they will send you a Private Message of where to source.
Next your B12 is woeful. You have to get checked for Pernicious Anaemia and I'd get your GP to test your Free T3.
We are better off 'Doing It Ourself' at least we know what makes us feel good. If we took too much of any thyroid hormones we'd soon reduce if we felt overdosed.
Before blood tests and levothyroxine were introduced in the 60's we were diagnosed on our clinical symptom s alone and not dictated to by blood tests and were given a trial of NDT - natural dessicated thyroid hormones which was first taken in 1892 and thus saved the life of that patient as well as others up to the 60's when the 'new' method was introduced.
You have to bring your B12 up to around 900 to 1,000 to prevent neurological damage and I'll give you a link. How doctors can ignore such a low result I don't know but most of them go by the 'range' if you are somewhere within that's fine to them whilst the patient deteriorates. Buy methylcobalamn B12 sublingual and most members source them from Amazon. I now don't buy Solgar as I found they didn't dissolve under tongue.
You can improve your health but it does take time.
You can get private blood tests (pin-prick from recommended labs) and the most important are Free T4 and Free T3 and I'll give you a link and you can see the reason why we have to know these.
Doctors have absolutely no idea or Endocrinologists how unwell and desperate it is to be taking thyroid hormone replacements and feeling worse than before we were diagnosed (most likely).
I am not medically qualified but had undiagnosed hypothyroidism for years but was diagnosed with other problems and had 'treatment' which was completely unnecessary.
We are always wise after an 'event' but we can well do without events and the aim of thyroid hormone replacement is to alleviate ALL clinical symptoms not give us more.