Re: too much methimazole
Endos are known in the thyroid patient community as generally inept with thyroid disease, especially hypOthyroidism. With hyperthyroidism, we must throw ourselves on their mercy, because it's even more tricky to treat than hypoT. GPs and internists usually want no part of treating hyperT.
That said, if this endo's arrogance is as you portray it, you will probably have to find another MD if you want to be optimally treated.
Is this guy testing not just your TSH, but your free T4 and free T3 as well? TSH is a pituitary hormone and only an indirect indication of thyroid status. Free T4/3 are the actual thyroid hormones, and they are what determine whether there will be symptoms or not.
If you have indeed gone hypo, it will show in the free Ts; they'll be below lab median. If your TSH is above 1.5-2.0, that's another sign. Do you have labs to share so we can help you interpret them?
Your dose is quite high, and there's every possibility your suspicion about going hypo is true. Educate yourself on proper treatment so that you'll get that which is best for you. Patient self-advocacy is vital when it comes to thyroid disease.
Best of luck to you.