Your doctor is a disgrace (my point of view), to keep a patient on a miserly dose of 50mcg of levothyroxine for years is completely unaware of the dangers he may put the patient in.
25mcg is even worse. He is doing as so many other doctors are doing in only going by the blood test results and adjusting willy/nilly in order to keep the test within a range. He/she doesn't realise that many of us need a very low or suppressed TSH to feel normal health. Instead there is unnecessary suffering and we are reliant on our doctors to know what's going on. If I take my car to a garage because something is wrong with my car, I expect the 'specialist' to have at least an idea of how to bring life back to it. Not send me off with a flea in my ear and say - there's plenty of oil it should be working. As you bump along the road stop/start till you get home.
Not satisfactory at all and I hope someone can recommend you a decent doctor who know that the problem begins in your neck not in the blood.
The following excerpt is informative:-
Our treatment team uses the TSH level only initially to help clarify a patient’s thyroid status. But during treatment, we completely ignore the level. The reason is that the TSH level is totally irrelevant to normalizing the patient’s whole body metabolism and relieving his or her suffering. The only clinical value of the TSH level is to see the effect of a particular dose of thyroid hormone on the pituitary gland’s "thyrotroph" (TSH-secreting) cells.
The thyrotroph cells are vastly more sensitive to thyroid hormone than are other body cells. Some endocrinologists argue that we know the ratio of two sensitivities: that is, the ratio of the sensitivity of the pituitary to a dose of thyroid hormone to the sensitivity of other tissues to that dose. From knowledge of that ratio, they argue, we can use the TSH to gauge the thyroid hormone dose that properly regulates the metabolism of all body cells.
Go to the question/answer on the following link - date November 28, 2003. The other questions will also be informative.